tests: allow to skip git rebase -p tests

The --preserve-merges mode of the git rebase command is on its way out, being superseded by the --rebase-merges mode. My plan is to contribute patches to deprecate the former in favor of the latter before long.

In the meantime, it seems a bit pointless to keep running the git rebase -p tests, in particular in the Windows phase of the automated testing. In preparation for skipping those tests, this patch series starts out by decoupling test cases so that no non-rebase -p ones depend on side effects of rebase -p ones, and it concludes by a patch that allows skipping the rebase -p ones by setting the environment variable GIT_TEST_SKIP_REBASE_P.

In a quick 'n dirty test, skipping the rebase -p tests seems to shave off about 8 minutes from the 1h20 running time of the test suite on Windows (without git svn tests, we skip them for a long time already, as they are really, really slow on Windows).

Johannes Schindelin (3):
t3404: decouple some test cases from outcomes of previous test cases
t3418: decouple test cases from a previous rebase -p test case
tests: optionally skip git rebase -p tests

 t/t3404-rebase-interactive.sh             | 23 ++++++++-------
 t/t3408-rebase-multi-line.sh              |  2 +-
 t/t3409-rebase-preserve-merges.sh         |  5 ++++
 t/t3410-rebase-preserve-dropped-merges.sh |  5 ++++
 t/t3411-rebase-preserve-around-merges.sh  |  5 ++++
 t/t3412-rebase-root.sh                    | 12 ++++----
 t/t3414-rebase-preserve-onto.sh           |  5 ++++
 t/t3418-rebase-continue.sh                |  5 ++--
 t/t3421-rebase-topology-linear.sh         | 36 +++++++++++------------
 t/t3425-rebase-topology-merges.sh         |  5 ++++
 t/t5520-pull.sh                           |  6 ++--
 t/t7505-prepare-commit-msg-hook.sh        |  2 +-
 t/t7517-per-repo-email.sh                 |  6 ++--
 t/test-lib.sh                             |  4 +++
 14 files changed, 78 insertions(+), 43 deletions(-)

base-commit: 4ede3d42dfb57f9a41ac96a1f216c62eb7566cc2
Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-63%2Fdscho%2Fsplit-out-rebase-p-tests-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-63/dscho/split-out-rebase-p-tests-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/63

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