Explicitly fflush stdout in git clean

This is yet another patch that was funneled through a Git for Windows PR,
read: it has been battle-tested.

Of course, the current iteration of this patch series has not been battle-tested, so please do review carefully, so that we can prevent bugs from slipping in during the review process.

Changes since v2:

* Fixed the capitalization of "THerefore" in the commit message.

Changes since v1:

* Added a preparatory patch that refactors all interactive input reading via strbuf_getline(..., stdin).
* Adjusted the patch and its commit message accordingly.

Johannes Schindelin (1):
Refactor code asking the user for input interactively

마누엘 (1):
Explicitly fflush stdout before expecting interactive input

 add-interactive.c |  4 ++--
 add-patch.c       |  4 ++--
 builtin/clean.c   | 14 ++++----------
 prompt.c          | 12 ++++++++++++
 prompt.h          |  2 ++
 shell.c           |  4 ++--
 6 files changed, 24 insertions(+), 16 deletions(-)

base-commit: 9fadedd637b312089337d73c3ed8447e9f0aa775
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-755%2Fdscho%2Ffflush-in-git-clean-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-755/dscho/fflush-in-git-clean-v3
Pull-Request: https://github.com/git/git/pull/755

Range-diff vs v2:

1: 9d2ee78a9e4 ! 1: 072f95090ae Refactor code asking the user for input interactively
@@ Commit message
beginning and at the end of the answer, instead of trimming only the end (as the caller in add-patch.c does).

- THerefore, technically speaking, we change behavior in this patch. At
+ Therefore, technically speaking, we change behavior in this patch. At
the same time, it can be argued that this is actually a bug fix.

2: d3949e42004 = 2: 063d2aaa401 Explicitly fflush stdout before expecting interactive input

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