vreportf: Fix interleaving issues, remove 4096 limitation

This fixes t5516 on Windows. For detailed explanation please refer to code comments in this commit.

There was a lot of back-and-forth already in vreportf(): d048a96e (2007-11-09) - 'char msg[256]' is introduced to avoid interleaving 389d1767 (2009-03-25) - Buffer size increased to 1024 to avoid truncation 625a860c (2009-11-22) - Buffer size increased to 4096 to avoid truncation f4c3edc0 (2015-08-11) - Buffer removed to avoid truncation b5a9e435 (2017-01-11) - Reverts f4c3edc0 to be able to replace control chars before sending to stderr

This fix attempts to solve all issues:

1) avoid multiple fprintf() interleaving 2) avoid truncation 3) avoid char interleaving in fprintf() on some platforms 4) avoid buffer block interleaving when output is large 5) avoid Out-of-order messages 6) replace control characters in output

Other commits worthy of notice: 9ac13ec9 (2006-10-11) - Another attempt to solve interleaving. This is seemingly related to d048a96e. 137a0d0e (2007-11-19) - Addresses out-of-order for display() 34df8aba (2009-03-10) - Switches xwrite() to fprintf() in recv_sideband() to support UTF-8 emulation eac14f89 (2012-01-14) - Removes the need for fprintf() for UTF-8 emulation, so it's safe to use xwrite() again 5e5be9e2 (2016-06-28) - recv_sideband() uses xwrite() again

Alexandr Miloslavskiy (1):
vreportf: Fix interleaving issues, remove 4096 limitation

 usage.c | 154 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 148 insertions(+), 6 deletions(-)

base-commit: d966095db01190a2196e31195ea6fa0c722aa732
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-407%2FSyntevoAlex%2F%230194_t5516_fixes-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-407/SyntevoAlex/#0194_t5516_fixes-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/407

Range-diff vs v1:

1: 5fd06fa881 ! 1: 54f0d6f6b5 vreportf: Fix interleaving issues, remove 4096 limitation
@@ -23,12 +23,12 @@

Other commits worthy of notice:
9ac13ec9 (2006-10-11) - Another attempt to solve interleaving.
- This is seemingly related to d048a96e.
+ This is seemingly related to d048a96e.
137a0d0e (2007-11-19) - Addresses out-of-order for display() 34df8aba (2009-03-10) - Switches xwrite() to fprintf() in recv_sideband()
- to support UTF-8 emulation
+ to support UTF-8 emulation
eac14f89 (2012-01-14) - Removes the need for fprintf() for UTF-8 emulation,
- so it's safe to use xwrite() again
+ so it's safe to use xwrite() again
5e5be9e2 (2016-06-28) - recv_sideband() uses xwrite() again

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