patch: handle filenames with trailing spaces

I have no idea if this is *actually* supported by the patch file format, but at
least when reading from a patch file created by running `hg shelve`, it is
written out such that there's a trailing space after the second (`b`) filename.
When we read the patch file, we remove the space before parsing the filenames,
so it doesn't end up matching the other sources of what files are in the shelve.

We observed this internally due to a wrapper around unshelve that called into
patch.changedfiles, but `hg patch` is able to reproduce the issue as well, so
I've included both tests.

Differential Revision: https://phab.mercurial-scm.org/D9729

tests/test-shelve.t

@@ -1512,3 +1512,26 b' Abort unshelve while merging (issue5123)'
   $ hg unshelve -i --keep
   abort: --keep on --interactive is not yet supported
   [255]
+
+  $ hg update -q --clean .
+
+Test that we can successfully shelve and unshelve a file with a trailing space
+in the filename. Such filenames are supposedly unsupported on Windows, so we
+wrap it in the no-windows check. Also test `hg patch` of the .patch file
+produced by `hg shelve`.
+#if no-windows
+  $ echo hi > 'my filename '
+  $ hg add 'my filename '
+  warning: filename ends with ' ', which is not allowed on Windows: 'my filename '
+  $ hg shelve
+  shelved as default-01
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ cp .hg/shelved/default-01.patch test_patch.patch
+  $ hg unshelve
+  unshelving change 'default-01'
+  $ cat 'my filename '
+  hi
+  $ hg update -q --clean .
+  $ hg patch -p1 test_patch.patch
+  applying test_patch.patch
+#endif