Minor buffer.c style cleanups
Remove FEAT_MOUSE_JSB

This is never built and references some obscure jsb terminal
Merge pull request #934 from fornwall/remove-FEAT_MOUSE_JSB

Remove FEAT_MOUSE_JSB
Merge pull request #998 from war1025/dev/buffer_cleanup

Minor buffer.c style cleanups
eval: re-remove USE_CR #1002

It was already removed in 01ca460 and I erroneously introduced it again in
PR #978.
Units: Move NULL, OK, and FAIL to helpers.moon. #982
eval: re-add has('mac') and has('macunix') #976

They were removed but they can be handy to separate some things to do at
startup in a .vimrc for example.
doc: Remove 'textmode'

by @mhinz
runtime: Remove 'textauto'
doc: Remove "h" flag of 'highlight' option

HLF_H is an obsolete flag and got replaced by HLF_E.

From: Marco Hinz <mh.codebro@gmail.com>
vim-patch:7.4.235

Problem:    It is not easy to get the full path of a command.
Solution:   Add the exepath() function.

https://code.google.com/p/vim/source/detail?r=5ab2946f7ce560985830fbc3c453bb0f7a01f385
Update os_can_exe() unit tests.

patch 235 added a new argument to os_can_exe(), the path of the
executable. Update the tests to verify the output as well.