Force listingblocks to be monospaced in manpages

Force listingblocks to be monospaced in manpages

For the html output we can use a stylesheet to make sure that the
listingblocks are presented in a monospaced font.  For the manpages do
it manually by inserting a ".ft C" before and ".ft" after the block in
question.

In order for these roff commands to get through to the manpage they
have to be element encoded to prevent quoting.

Signed-off-by: Julian Phillips <redacted>
Signed-off-by: Junio C Hamano <redacted>