mergestate: implement unresolvedcount() in terms of unresolved()
This simplifies the method slightly. It does create a full list of
paths while doing so, but it's not a lot of data anyway (besides, I
would think references to strings are no larger than (references to?)
True).
#if no-windows no-osx
$ mkdir -p xdgconf/hg
$ echo '[ui]' > xdgconf/hg/hgrc
$ echo 'username = foobar' >> xdgconf/hg/hgrc
$ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
$ unset HGRCPATH
$ hg config ui.username 2>/dev/null
foobar
#endif