Merge branch 'ab/test-2'

Merge branch 'ab/test-2'

* ab/test-2: (51 commits)
  tests: factor HOME=$(pwd) in test-lib.sh
  test-lib: use subshell instead of cd $new && .. && cd $old
  tests: simplify "missing PREREQ" message
  t/t0000-basic.sh: Run the passing TODO test inside its own test-lib
  test-lib: Allow overriding of TEST_DIRECTORY
  test-lib: Use "$GIT_BUILD_DIR" instead of "$TEST_DIRECTORY"/../
  test-lib: Use $TEST_DIRECTORY or $GIT_BUILD_DIR instead of $(pwd) and ../
  test: Introduce $GIT_BUILD_DIR
  cvs tests: do not touch test CVS repositories shipped with source
  t/t9602-cvsimport-branches-tags.sh: Add a PERL prerequisite
  t/t9601-cvsimport-vendor-branch.sh: Add a PERL prerequisite
  t/t7105-reset-patch.sh: Add a PERL prerequisite
  t/t9001-send-email.sh: convert setup code to tests
  t/t9001-send-email.sh: change from skip_all=* to prereq skip
  t/t9001-send-email.sh: Remove needless PROG=* assignment
  t/t9600-cvsimport.sh: change from skip_all=* to prereq skip
  lib-patch-mode tests: change from skip_all=* to prereq skip
  t/t3701-add-interactive.sh: change from skip_all=* to prereq skip
  tests: Move FILEMODE prerequisite to lib-prereq-FILEMODE.sh
  t/Makefile: Create test-results dir for smoke target
  ...

Conflicts:
	t/t6035-merge-dir-to-symlink.sh