rhg: in rhg cat cli, fix the long name of the --rev flag

Also tweak the help for the anonymous argument.

Differential Revision: https://phab.mercurial-scm.org/D11617

rust/rhg/src/commands/cat.rs

@@ -16,7 +16,7 b" pub fn args() -> clap::App<'static, 'sta"
             Arg::with_name("rev")
                 .help("search the repository as it is in REV")
                 .short("-r")
-                .long("--revision")
+                .long("--rev")
                 .value_name("REV")
                 .takes_value(true),
         )
@@ -26,7 +26,7 b" pub fn args() -> clap::App<'static, 'sta"
                 .multiple(true)
                 .empty_values(false)
                 .value_name("FILE")
-                .help("Activity to start: activity@category"),
+                .help("Files to output"),
         )
         .about(HELP_TEXT)
 }

tests/test-rhg.t

@@ -121,6 +121,8 b' Specifying revisions by changeset ID'
   file-3
   $ $NO_FALLBACK rhg cat -r cf8b83 file-2
   2
+  $ $NO_FALLBACK rhg cat --rev cf8b83 file-2
+  2
   $ $NO_FALLBACK rhg cat -r c file-2
   abort: ambiguous revision identifier: c
   [255]