Fix the infinite loop in kwhelp.e (when env var and inf file names match)

[jbs]

if there is an environment variable whose name matches the name of one of the INF files it references, like:
SET REXX=REXX+JSRXUTIL
where the first REXX is the name of an environment variable and the second is the name of an INF file, then kwhelp gets stuck in an infinite loop "thinking" both "REXX"'s are environment variable names.

[Andreas Schnellbacher]

Fixed by changeset r2632.