SetFromCmd - Set env from output of command. The command result will be

             returned to $RC, which regular "Set and backticks" won't do.

Usage: SetFromCmd NAME/A,GLOBAL/S,SAVE/S,COMMANDLINE/F/A

NAME: Name of the destination environment variable.

GLOBAL: Set if it should be a global environment variable, which

         normally is saved in ENV:. Default is to create a local

         environment variable in the current shell.

SAVE: Set if the environment variable should be saved in ENVARC:. This

         will also imply that it will be created as a global environment

         variable.

COMMANDLINE: The complete commandline to execute.

Example:

1> SetFromCmd REVISION aget http://uhc.driar.se/uhctools_revision TOSTDOUT

Relevant info:

• It will capture all output from the command, including SAS/C-style stderr

and AmigaOS4 ErrorOutput().

• If the executed command attempts to read from its stdin/Input(), the reads

will be forwarded to SetFromCmd's stdin/Input().