coverity/74717: FP: NULL Pointer Dereference

dynamic_buffer_ensure() allocates buf->data; add an assert to make this
clear to coverity.
vim-patch:7.4.450

Problem:    Not all commands that edit another buffer support the +cmd
	    argument.
Solution:   Add the +cmd argument to relevant commands. (Marcin Szamotulski)

https://code.google.com/p/vim/source/detail?r=v7-4-450
vim-patch:7.4.486

Problem:    Check for writing to a yank register is wrong.
Solution:   Negate the check. (Zyx).  Also clean up the #ifdefs.

https://code.google.com/p/vim/source/detail?r=v7-4-486
Transform global variable really_exiting into static.
coverity/90712: Remove unnecessary check for NULL.

** CID 90712:  Dereference after null check  (FORWARD_NULL)
/src/nvim/getchar.c: 3654 in check_abbr()

vim_strsave() never returns NULL, so q is never NULL. Removing the
NULL check for q should fix this warning.
Merge pull request #1741 from oni-link/fix_cid_90712

coverity/90712: Remove unnecessary check for NULL.
Merge pull request #1718 from jonaias/master

Transform global variable really_exiting into static.
Merge pull request #1725 from fwalch/vim-7.4.450

vim-patch:7.4.450
Merge pull request #1730 from fwalch/vim-7.4.486

vim-patch:7.4.486
Merge pull request #1684 from justinmk/coverity74717

[RFC] coverity/74717: FP: NULL Pointer Dereference