Move pg_upgrade from contrib/ to src/bin/

contrib/Makefile

doc/src/sgml/contrib.sgml

doc/src/sgml/filelist.sgml

doc/src/sgml/ref/allfiles.sgml

doc/src/sgml/ref/pgupgrade.sgml

doc/src/sgml/reference.sgml

src/bin/Makefile

src/bin/pg_upgrade/.gitignore

src/bin/pg_upgrade/IMPLEMENTATION

src/bin/pg_upgrade/Makefile

src/bin/pg_upgrade/TESTING

src/bin/pg_upgrade/check.c

src/bin/pg_upgrade/controldata.c

src/bin/pg_upgrade/dump.c

src/bin/pg_upgrade/exec.c

src/bin/pg_upgrade/file.c

src/bin/pg_upgrade/function.c

src/bin/pg_upgrade/info.c

src/bin/pg_upgrade/option.c

src/bin/pg_upgrade/page.c