Tell the 'less' pager to allow terminal escape sequences

The 'ToTerm' backend generates terminal escape sequences that
the 'less' pager does not display by default. The "-R" option
controls this, so pass it in the LESS environment variable
to avoid disturbing other pager invocations.

Bug-Debian: https://bugs.debian.org/758689
Patch-Name: debian/perldoc-less-R.diff