[PATCH 0 of 1] tonfa's suggestion for security fixes to contrib/vim/patchreview.*

[Manpreet Singh]

This patch implements the suggestions tonfa made for patchreview.vim contrib
on IRC. Namely it uses tempname() rather than my own custom filepath generation
logic for temporary files.

In addition it also has

1) Removed the need for DiffReviewCleanup/PatchReviewCleanup due to above
2) Better command execution error detection and display
3) Improved diff view and folding by ignoring modelines (tonfa ran into this)
4) Improved tab labels display

Please review and consider.

Thanks
Manpreet Singh