compression: display compression level in debugformat
Now that we have options to control the compression level, we teach `hg
debugformat` about them. This is a useful information when comparing
repositories.
Note that we have no trace of the compression level used to store existing
deltas. Actually, it would even varies from one delta to another. So we display
the currently set value.
#require docutils gettext
$ $TESTDIR/check-gendoc fr
checking for parse errors