pgsql: Tests for COMSPEC in the right place and supply a reasonable

Log Message:
-----------
Tests for COMSPEC in the right place and supply a reasonable shell
default on Win32.

Modified Files:
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pgsql/src/bin/psql:
command.c (r1.130 -> r1.131)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c.diff?r1=1.130&r2=1.131)