Adding two new options to the 'help' command:

 --show-aliases (-a) shows aliases for commands, as well as built-in commands
 --hide-user-defined (-u) hides user defined commands
by default 'help' without arguments does not show aliases anymore. to see them, add --show-aliases
to have only built-in commands appear, use 'help --hide-user-defined' ; there is currently no way to hide
built-in commands from the help output
'help command' is not changed by this commit, and help is shown even if command is an alias and -a is not specified

llvm-svn: 139377