Make pgxs build executables with the right suffix.

Complaint and patch from Zoltán Böszörményi.

When cross-compiling, the native make doesn't know
about the Windows .exe suffix, so it only builds with
it when explicitly told to do so.

The native make will not see the link between the target
name and the built executable, and might this do unnecesary
work, but that's a bigger problem than this one, if in fact
we consider it a problem at all.

Back-patch to all live branches.
Modernize string literal syntax in tutorial example.

Un-double the backslashes in the LIKE patterns, since
standard_conforming_strings is now the default.  Just to be sure, include
a command to set standard_conforming_strings to ON in the example.

Back-patch to 9.1, where standard_conforming_strings became the default.

Josh Kupershmidt, reviewed by Jeff Janes
Use SET TRANSACTION READ ONLY in pg_dump, if server supports it.

This currently does little except serve as documentation.  (The one case
where it has a performance benefit, SERIALIZABLE mode in 9.1 and up, was
already using READ ONLY mode.)  However, it's possible that it might have
performance benefits in future, and in any case it seems like good
practice since it would catch any accidentally non-read-only operations.

Pavan Deolasee