help: provide help of bad alias without executing aliascmd()
The output is slightly changed because of minirst formatting. Previously,
ui.pushbuffer() had no effect because "badalias" message was written to stderr.
"if not unknowncmd" should no longer be needed because there's no call loop.
http://example.com/no/anchor, branches: (None, [])
http://example.com/an/anchor, branches: ('foo', [])
http://example.com/no/anchor/branches, branches: (None, ['foo'])
http://example.com/an/anchor/branches, branches: ('bar', ['foo'])
http://example.com/an/anchor/branches-None, branches: ('foo', [])
http://example.com/, branches: (None, [])
http://example.com/, branches: (None, [])
http://example.com/, branches: ('foo', [])