Merge branch 'jk/save-getenv-result'

There were many places the code relied on the string returned from getenv() to be non-volatile, which is not true, that have been corrected. * jk/save-getenv-result: builtin_diff(): read $GIT_DIFF_OPTS closer to use merge-recursive: copy $GITHEAD strings init: make a copy of $GIT_DIR string config: make a copy of $GIT_CONFIG string commit: copy saved getenv() result get_super_prefix(): copy getenv() result