Improve documentation for merging
Merge pull request #2132 from ethomson/merge_doc

Improve documentation for merging
Staticize file-local variables
Avoid casting warning
Prevent icc warning
Use a portable cast
Merge pull request #2134 from libgit2/ben/icc

Fix Intel compiler warnings
Move system directory cache out of utils
Include stdarg.h for the va_copy test
Remove now-duplicated stdarg.h include
Merge pull request #2139 from ethomson/va_copy_warning

Include stdarg.h for the va_copy test
Merge pull request #2138 from ethomson/sysdir

Move system directory cache out of utils