Bug: Case-insensitive filesystems can cause merge and checkout problems

[David Turner <dturner@twopensource.com>]

By default, git sets core.ignorecase=true when git init or git clone
is run on a machine with a case-insensitive filesystem.  Here's a
test-case for some problems that this causes:

git checkout master
touch TestCase
git add TestCase
git commit -m 'add TestCase'
git checkout -b with-camel
touch foo
git add foo
git commit -m 'intervening commit'
git checkout master
git rm TestCase
touch testcase
git add testcase
git commit -m 'rename to testcase'
git checkout with-camel
git merge master -m 'merge'

One would expect a clean working copy at this point, but in fact, the
file 'testcase' will be deleted.

With core.ignorecase=false, we get a different failure.  The
penultimate command fails with:
$ git checkout with-camel
error: The following untracked working tree files would be overwritten
by checkout:
        TestCase
Please move or remove them before you can switch branches.
Aborting

Of course, there is no untracked working tree file by that name; there
is a tracked working tree file named testcase (all-lowercase).