pgsql: Use (unsigned char) cast in argument of pg_tolower().

Log Message:
-----------
Use (unsigned char) cast in argument of pg_tolower(). Maybe it works on
Windows without that, but we shouldn't put bad examples where people might
copy them. Also, reformat slightly to improve the odds that pgindent
won't go nuts on this.

Modified Files:
--------------
pgsql/src/port:
path.c (r1.77 -> r1.78)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/port/path.c?r1=1.77&r2=1.78)