add HGRCPATH env var, list of places to look for hgrc files.
if set, override default hgrc search path.
if empty, only .hg/hgrc of current repo read.
for each element, if directory, all entries in directory with end in
".rc" are added to path. else, element is added to path.
big thing about this change is that user "~/.hgrc" and system hgrc not
longer breaks tests. run-tests makes HGRCPATH empty now.
abort: impossible time zone offset: 4444444
transaction abort!
rollback completed
abort: invalid date: '1\t15.1'
transaction abort!
rollback completed
abort: invalid date: 'foo bar'
transaction abort!
rollback completed
abort: invalid date: ' 1 4444'
transaction abort!
rollback completed
abort: date exceeds 32 bits: 111111111111
transaction abort!
rollback completed
abort: No such file or directory: .../test/bar