Merge branch 'bp/rename-test-env-var'

Some environment variables that control the runtime options of Git
used during tests are getting renamed for consistency.

* bp/rename-test-env-var:
t0000: do not get self-test disrupted by environment warnings
preload-index: update GIT_FORCE_PRELOAD_TEST support
read-cache: update TEST_GIT_INDEX_VERSION support
fsmonitor: update GIT_TEST_FSMONITOR support
preload-index: use git_env_bool() not getenv() for customization
t/README: correct spelling of "uncommon"

diff --cc Makefile
Simple merge

diff --cc preload-index.c
Simple merge

diff --cc t/README
index 4d8dbc7c5f5800bb838a09a8ca87fab8a3de72ab,5670c7aad0ad10dcc55c8a6923b19a362c365776..d8b04c35c01344534776a01e85b7f5f4f988cc62
--- 1/t/README
--- 2/t/README
+++ b/t/README
@@@ -319,14 -319,17 +319,25 @@@ GIT_TEST_OE_DELTA_SIZE=<n> exercises th
  path where deltas larger than this limit require extra memory
  allocation for bookkeeping.
  
 +GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES=<boolean> checks that cache-tree
 +records are valid when the index is written out or after a merge. This
 +is mostly to catch missing invalidation. Default is true.
 +
 +GIT_TEST_COMMIT_GRAPH=<boolean>, when true, forces the commit-graph to
 +be written after every 'git commit' command, and overrides the
 +'core.commitGraph' setting to true.
 +
+ GIT_TEST_FSMONITOR=$PWD/t7519/fsmonitor-all exercises the fsmonitor
+ code path for utilizing a file system monitor to speed up detecting
+ new or changed files.
+ 
+ GIT_TEST_INDEX_VERSION=<n> exercises the index read/write code path
+ for the index version specified.  Can be set to any valid version
+ (currently 2, 3, or 4).
+ 
+ GIT_TEST_PRELOAD_INDEX=<boolean> exercises the preload-index code path
+ by overriding the minimum number of cache entries required per thread.
+ 
  Naming Tests
  ------------
  

diff --cc t/t0000-basic.sh
Simple merge

diff --cc t/t1700-split-index.sh
Simple merge

diff --cc t/t7519-status-fsmonitor.sh
Simple merge

diff --cc t/test-lib.sh
Simple merge