add --config global option. allows to set hgrc option on command line.
syntax: --config section.name=value
also add new test-globalopts to test all global options in one place.
#!/bin/sh
hg init
python -c 'print "confuse str.splitlines\nembedded\rnewline"' > a
hg ci -Ama -d '1 0'
echo clean diff >> a
hg ci -mb -d '2 0'
hg diff -r0 -r1