[PATCH 0 of 2] Give mq qimport a -p/--strip option

[Brendan Cully]

This patch series gives qimport a --strip flag. The first patch
abstracts the patch header rewriting code in qrefresh, and the second
patch adds -p to the qimport command. When used, qimport adds a
'MQStrip' header to the patch as it copies it. qpush passes the value
of this header to patch, and qrefresh removes the header and uses the
default -p1 setting. This fixes issue311.