Add utility functions to plperl [PATCH]

This is the first of the patches to be split out from the former 'plperl
feature patch 1'.

Changes in this patch:

- Added utility functions: quote_literal, quote_nullable, quote_ident,
encode_bytea, decode_bytea, looks_like_number,
encode_array_literal, encode_array_constructor.

- Stored procedure subs are now given names ($name__$oid).
This is invisible to PL/Perl stored procedures but makes
tools like Devel::NYTProf and Devel::Cover _much_ more useful.

- Warnings no longer have an extra newline in the NOTICE text.

- Corresponding documentation changes in plperl.sgml, plus:
Removed some trailing whitespace.
Made some examples use more idiomatic perl.
Added the missing ', arguments' to docs of spi_exec_prepared().

- Assorted minor changes
Various minor optimizations like pre-growing data structures.
Makes proper use of the recently updated ppport.h.

Tim.