largefiles: cleanup of warnings on errors getting largefiles
Especially the "no default or default-push path set in hgrc" was often very
misleading and didn't give any hint where it actually was looking.
A long error messages is better than several multi-line messages.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a