Various config and option improvements.

Various config and option improvements.

- Various aspects of the Makefile are not configurable by setting
  macros on commandline or in environment
- new config.h file to allow various tunables like daemon uid and
  path to record current mapping table.
- new commandline to:
   Allow foreground running with syslog logging (-F)
   Change the file in which the mapping is stored (-f)
   Specify the username that portmap should run as (-U).

Signed-off-by: Neil Brown <neilb@suse.de>