pgsql: Reorganize XSLT stylesheet support.

Log Message:
-----------
Reorganize XSLT stylesheet support.  Put common things into a separate
file (instead of repeating), add XSL-FO stylesheet and appropriate make
rules.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        Makefile (r1.82 -> r1.83)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/Makefile.diff?r1=1.82&r2=1.83)
        stylesheet-hh.xsl (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/stylesheet-hh.xsl.diff?r1=1.1&r2=1.2)
        stylesheet.xsl (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/stylesheet.xsl.diff?r1=1.2&r2=1.3)

Added Files:
-----------
    pgsql/doc/src/sgml:
        stylesheet-common.xsl (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/stylesheet-common.xsl?rev=1.1&content-type=text/x-cvsweb-markup)
        stylesheet-fo.xsl (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/stylesheet-fo.xsl?rev=1.1&content-type=text/x-cvsweb-markup)