man: allow nroff and tbl commands be overridden; unmangle writing to files

man: allow nroff and tbl commands be overridden; unmangle writing to files

Parse this in config files:
	 DEFINE col ...
	 DEFINE tbl ...
	 DEFINE nroff ...
Add width options to nroff command line.
Use "tbl", not "gtbl", as default tbl command.
Export GROFF_NO_SGR=1 and use "col -b -p -x" instead of pager when writing to file.

function                                             old     new   delta
man_main                                             735     863    +128
if_redefined                                           -      64     +64
show_manpage                                         199     169     -30
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/1 up/down: 192/-30)           Total: 162 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>