sparse: consolidate common code for writing sparse config
In 3 functions we were writing the sparse config and updating the
working directory. In two of them we had a transaction-like process
for restoring the sparse config in case of wdir update fail.
Because the pattern is common, we've already made mistakes, and the
complexity will increase in the near future, let's consolidate the
code into a reusable function.
As part of this refactor, we end up reading the "sparse" file twice
when updating it. This is a bit sub-optimal. But I don't think it
is worth the code complexity to pass around the variables to avoid
the redundancy.
Differential Revision: https://phab.mercurial-scm.org/D109
syntax: glob
*.elc
*.tmp
*.orig
*.rej
*~
*.mergebackup
*.o
*.so
*.dll
*.exe
*.pyd
*.pyc
*.pyo
*$py.class
*.swp
*.prof
*.zip
\#*\#
.\#*
tests/.coverage*
tests/.testtimes*
tests/.hypothesis
tests/hypothesis-generated
tests/annotated
tests/*.err
tests/htmlcov
build
contrib/chg/chg
contrib/hgsh/hgsh
contrib/vagrant/.vagrant
contrib/docker/debian-*
contrib/docker/ubuntu-*
dist
packages
doc/common.txt
doc/*.[0-9]
doc/*.[0-9].txt
doc/*.[0-9].gendoc.txt
doc/*.[0-9].{x,ht}ml
MANIFEST
MANIFEST.in
patches
mercurial/__modulepolicy__.py
mercurial/__version__.py
mercurial/hgpythonlib.h
mercurial.egg-info
.DS_Store
tags
cscope.*
.idea/*
.asv/*
i18n/hg.pot
locale/*/LC_MESSAGES/hg.mo
hgext/__index__.py
# Generated wheels
wheelhouse/
syntax: regexp
^\.pc/
^\.(pydev)?project
# hackable windows distribution additions
^hg-python
^hg.py$