windows: add an experimental option for long paths support This commit adds an experimental --long-paths-support flag to build_hgexe on Windows. It is off by default, but when supplied, causes setup.py to embed some XML into the generated hg.exe, which in turn tells Windows to allow this exe to use long paths (given that the appropriate registry setting is enabled as well). This was tested on Windows 10 14393 and 15063. This commit introduces a badly-named initialize_options function, but its name is dictated by distutils, rather than chosen. # no-check-commit

running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset:   0:0e4634943879
user:        test
date:        Sat Jan 01 00:00:00 2000 +0000
summary:     commit1

result: None
running: log -r tip
changeset:   1:45589e459b2e
tag:         tip
user:        test
date:        Sun Jan 02 00:00:00 2000 +0000
summary:     commit2

result: None