pgsql-server: Tighened up syntax checking of array input processing

Log Message:
-----------
Tighened up syntax checking of array input processing considerably. Junk that
was previously allowed in odd places with odd results now causes an ERROR.
Also changed behavior with respect to whitespace -- trailing whitespace is
now ignored as well as leading whitespace (which has always been ignored).

Documentation updated to reflect change in whitespace handling. Also some
refactoring to what I believe is a more sensible order of several paragraphs.

Modified Files:
--------------
    pgsql-server/doc/src/sgml:
        array.sgml (r1.36 -> r1.37)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/array.sgml.diff?r1=1.36&r2=1.37)
    pgsql-server/src/backend/utils/adt:
        arrayfuncs.c (r1.106 -> r1.107)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/adt/arrayfuncs.c.diff?r1=1.106&r2=1.107)