closes #7239

The old behaviour was to set CMAKE_INSTALL_MANDIR to /usr/local/man
when MANPREFIX wasn't defined. This caused mismatching installation
paths when the installation prefix wasn't /usr/local.

This fix explicitely checks that the prefix is /usr/local to change
the value of CMAKE_INSTALL_MANDIR, and uses the default behaviour
otherwise, as /usr/local is the exception rather than the norm
(as per man hier(7)).

This should have been included in #6547 as part of vim-patch:7.4.2152.

Closes #7352

Handling of process exit is still broken.  It detects the moment when the
child process exits, then quickly stops polling for process output.  It
should continue polling for output until the agent has scraped all of the
process' output.  This problem is easy to notice by running a command like
"dir && exit", but even typing "exit<ENTER>" can manifest the problem --
the "t" might not appear.

winpty's Cygwin adapter handles shutdown by waiting for the agent to close
the CONOUT pipe, which it does after it has scraped the child's last
output.  AFAIK, neovim doesn't do anything interesting when winpty closes
the CONOUT pipe.

Tests that check localized error messages need a stable locale, else
errors like this occur:

    [  FAILED  ] 2 tests, listed below:
    [  FAILED  ] ...npack/file/vim/neovim/test/functional/eval/null_spec.lua @ 29: NULL list is accepted as an empty list by writefile()
    ...npack/file/vim/neovim/test/functional/eval/null_spec.lua:30: Expected objects to be the same.
    Passed in:
    (string) '
    E484: Cannot open file Xtest-functional-viml-null'
    Expected:
    (string) '
    E484: Can't open file Xtest-functional-viml-null'

    stack traceback:
            ...npack/file/vim/neovim/test/functional/eval/null_spec.lua:30: in function <...npack/file/vim/neovim/test/functional/eval/null_spec.lua:29>

    [  FAILED  ] ...k/file/vim/neovim/test/functional/ex_cmds/write_spec.lua @ 81: :write errors out correctly
    ...k/file/vim/neovim/test/functional/ex_cmds/write_spec.lua:97: Expected objects to be the same.
    Passed in:
    (string) 'Vim(write):E510: Cannot make backup file (add ! to override)'
    Expected:
    (string) 'Vim(write):E510: Can't make backup file (add ! to override)'

    stack traceback:
            ...k/file/vim/neovim/test/functional/ex_cmds/write_spec.lua:97: in function <...k/file/vim/neovim/test/functional/ex_cmds/write_spec.lua:81>

     10 SKIPPED TESTS
     2 FAILED TESTS
    -- Output to stderr:
    2017/07/29 00:41:32 ERROR 31133/open_log_file:170: Logging to stderr, failed to open $NVIM_LOG_FILE: Xtest-startup-xdg-logpath/nvim/log
    2017/07/29 00:41:32 WARN  31133/call_set_error:815: RPC: ch 1 was closed by the client

    CMake Error at /home/shlomif/Download/unpack/file/vim/neovim/cmake/RunTests.cmake:50 (message):
      Running functional tests failed with error: 1.

    FAILED: CMakeFiles/functionaltest
    cd /home/shlomif/Download/unpack/file/vim/neovim/build && /usr/bin/cmake -DBUSTED_PRG=/home/shlomif/Download/unpack/file/vim/neovim/.deps/usr/bin/busted -DLUA_PRG=/home/shlomif/Download/unpack/file/vim/neovim/.deps/usr/bin/luajit -DNVIM_PRG=/home/shlomif/Download/unpack/file/vim/neovim/build/bin/nvim -DWORKING_DIR=/home/shlomif/Download/unpack/file/vim/neovim -DBUSTED_OUTPUT_TYPE=nvim -DTEST_DIR=/home/shlomif/Download/unpack/file/vim/neovim/test -DBUILD_DIR=/home/shlomif/Download/unpack/file/vim/neovim/build -DTEST_TYPE=functional -DSYSTEM_NAME=Linux -P /home/shlomif/Download/unpack/file/vim/neovim/cmake/RunTests.cmake
    ninja: build stopped: subcommand failed.
    Makefile:102: recipe for target 'functionaltest' failed
    make: *** [functionaltest] Error 1

When neovim is dynamically linked against jemalloc on OSX, users are
hitting the deadlock described in jemalloc/jemalloc#895.

lua: Add paths from &runtimepath to package.path and package.cpath

- Do not delete it: may need to inspect it after tests finished.
- Avoids writing to stderr in cases where the test-local $XDG_DATA_HOME
  was not created yet.

https://svnweb.freebsd.org/ports/head/editors/neovim/Makefile?revision=428479&view=markup#l28

Closes #6771