Add ui.strict config item.
This turns off command matching by unambiguous prefix, and is a good
thing if you want to write future-proof scripts.
This fixes issue 314.
#!/bin/sh
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
ls
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
hg co 0
# B should disappear
ls