pgsql: Another round of editorialization on the text search

Log Message:
-----------
Another round of editorialization on the text search documentation.
Notably, standardize on using "token" for the strings output by a parser,
while "lexeme" is reserved for the normalized strings produced by a
dictionary.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        textsearch.sgml (r1.19 -> r1.20)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/textsearch.sgml?r1=1.19&r2=1.20)
    pgsql/doc/src/sgml/ref:
        alter_tsdictionary.sgml (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/alter_tsdictionary.sgml?r1=1.2&r2=1.3)