...in order to retrieve highlights.

Added test/functional/api/highlight_spec.lua
HL_NORMAL is not really a good name, since it's more like an empty attribute than the normal's one.
If one pays attention, syn_cterm_attr2entry is never called with attr=0 because it's always special cased before.
I suggest in subsequent PRs we remove the ATTR_OFF and just insert an EMPTY ATTR/RESET_ATTR/UNINITIALIZED for id 0.

As of unibilium 1.2.1, directly manipulating unibi_var_t is deprecated.

    ../src/nvim/tui/tui.c: In function 'update_attrs':
    ../src/nvim/tui/tui.c:321:7: warning: 'i' is deprecated: use unibi_var_from_num or unibi_num_from_var instead [-Wdeprecated-declarations]
           data->params[0].i = (fg >> 16) & 0xff;  // red
           ^~~~
    In file included from ../src/nvim/tui/tui.c:12:0:
    /usr/include/unibilium.h:632:9: note: declared here
         int i   UNIBI_DEPRECATED("use unibi_var_from_num or unibi_num_from_var instead");
             ^

All use should go through unibi_{num,str}_from_var and
unibi_var_from_{num,str}.  Wrap access of unibi_var_t behind a new
UNIBI_SET_NUM_VAR macro which uses the new functions when they're
available.

closes #4840
closes #6164

closes #7235

iTerm2 got its own entry in Thomas Dickey's terminfo.src on 2017-08-16.
Make sure that the new entry is handled in the same way as the old entry.

closes #7209
closes #7214

When using an index returned by unibi_add_ext_str() we should
always use unibi_get_ext_str() and not rely on the index being
lower than unibi_string_begin_.

Closes #7206

Fix linuxvt cursor shape codes
Fix konsole cursor_shapes (even when inside tmux)
Do not trust old VTE terminal lies

Closes #6978
Closes #7002
Closes #7049

32396b5879b429def1c48948069c55366d41b9be add length checks to
TERMINAL_FAMILY/STARTS_WITH to ensure memcmp() wouldn't read past the
end of the string.  However, "term" was copy/pasted from TERMINAL_FAMILY
so STARTS_WITH() was unnecessarily reading the, potentially NULL, term
variable.

Closes #7041