pgsql: Contrib build fixes: - add some additional files to the dbmirror

Log Message:
-----------
Contrib build fixes:

- add some additional files to the dbmirror install (approved by
ssinger)

- add a makefile for contrib/mysql, and add mysql to the list of
contribs build by default

- use xml2-config to pickup -I flags for libxml2 in contrib/xml and
contrib/xml2

Original work from Martin Pitt of Debian, minor cleanups by Neil
Conway.

Modified Files:
--------------
pgsql/contrib:
Makefile (r1.51 -> r1.52)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/Makefile.diff?r1=1.51&r2=1.52)
pgsql/contrib/dbmirror:
Makefile (r1.3 -> r1.4)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dbmirror/Makefile.diff?r1=1.3&r2=1.4)
pgsql/contrib/mysql:
mysql2pgsql (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/mysql/mysql2pgsql.diff?r1=1.2&r2=1.3)
pgsql/contrib/xml:
Makefile (r1.9 -> r1.10)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/xml/Makefile.diff?r1=1.9&r2=1.10)
pgsql/contrib/xml2:
Makefile (r1.4 -> r1.5)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/xml2/Makefile.diff?r1=1.4&r2=1.5)

Added Files:
-----------
pgsql/contrib/mysql:
Makefile (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/mysql/Makefile?rev=1.1&content-type=text/x-cvsweb-markup)