Move files from src/ to src/nvim/.
- src/nvim/ becomes the new root dir for nvim executable sources.
- src/libnvim/ is planned to become root dir of the neovim library.

reverting broad cosmetic/style change because:
- increases merge-conflicts
- increases overhead of merging upstream Vim patches
- reasons for change are ambiguous, so default to no change

Rename `shorten_fname` -> `path_shorten_fname`
Rename `shorten_fname1` -> `path_shorten_fname_if_possible`

Clean up the use of list_append_dict and remove error checks.

Use `xcalloc` instead.
Inline `alloc_tv` and `alloc_string_tv` in eval.c

Today's compilers generate shift instructions to perform division and
multiplications by powers of 2 [1]. `(x >> 1)` looks straightforward enough, but
if x is signed the code will fail when x < 0. The compiler knows better: use
`x / 2`.

That's why we have code like this:

    (long)((long_u)Rows >> 1))

instead of the cleaner version that generates the same or better machine code:

    Rows / 2

[1] http://goo.gl/J4WpG7

quickfix.c

 - ll_new_list
 - ll_get_or_alloc_list

regex_nfa.c

 - realloc_post_list -> EMIT -> nfa_emit_equi_class
 - nfa_regcomp_start

Use xrealloc() in realloc_post_list() (regexp_nfa.c)

  Test plan: force a call to realloc_post_list() for every use of the EMIT macro;
  open nvim and test regexp search.