Bug 21439

Cleaned up the Makefile to be easier to read and maintain. The port now uses
the ${CFLAGS} setting from /etc/make.conf which was previously ignored.
Updated the PLIST file to accurately reflect what's actually installed.
Removed man files from PLIST since they don't belong there. Changed
	@dirrm /var/spool/postfix
to
	@unexec rm -rf /var/spool/postfix
in PLIST since in practice a) the original line was trying to remove
/usr/local//var/spool/postfix which did not exist and b) @dirrm wouldn't
work even if it were pointing at the correct path because Postfix creates a
number of subdirectories which are not accounted for in PLIST and which may
not be empty even if they were accounted for.

Rewrote the do-install target to use ${INSTALL_PROGRAM}, ${INSTALL_SCRIPT}
${INSTALL_DATA} and ${INSTALL_MAN} macros where appropriate. Added an
install for ${PREFIX}/etc/postfix/postfix-script which was missing and is
required by the postfix command. Added a check for NOPORTDOCS before
installing HTML documentation.

Fixed the call to ${PKGDIR}/INSTALL in the pre-install target and added an
analogous post-install target. In ${PKGDIR}/INSTALL the permissions for
postdrop should be 2555 not 2755 since ${BINMODE} used by ${INSTALL_PROGRAM}
is 0555. Now that post-install handles the chown and chmod for postdrop
there is no need for special handling of this issue elsewhere in the Makefile
so that was removed. Finally added a call to ${PKG_PREFIX}/sbin/postfix check
in ${PKGDIR}/INSTALL to create all the /var/spool/postfix/* subdirectories
at install time instead of when Postfix is first run.

Hope this helps and actually gets committed unlike a similar PR I sent months
ago for the postfix stable port.

How-To-Repeat: 
	cd /usr/ports/mail/postfix-current && make install