minifileset: note the unsupported file pattern when raising a parse error
This was useful in debugging, because I stupidly quoted it out of habit from the
command line. This isn't a great example that clearly shows the problem, but I
don't know how to improve it. The problem *is* obvious once a complex statement
or a clearly bogus string is used.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}