shelve: improve help text for --patch and --stat

It's not currently obvious why "hg shelve -p" fails, since -p doesn't take an argument.

Differential Revision: https://phab.mercurial-scm.org/D3949

hgext/shelve.py

@@ -1011,11 +1011,14 b' def _dounshelve(ui, repo, *shelved, **op'
           ('n', 'name', '',
            _('use the given name for the shelved commit'), _('NAME')),
           ('p', 'patch', None,
-           _('show patch')),
+           _('output patches for changes (provide the names of the shelved '
+             'changes as positional arguments)')),
           ('i', 'interactive', None,
            _('interactive mode, only works while creating a shelve')),
           ('', 'stat', None,
-           _('output diffstat-style summary of changes'))] + cmdutil.walkopts,
+           _('output diffstat-style summary of changes (provide the names of '
+             'the shelved changes as positional arguments)')
+           )] + cmdutil.walkopts,
          _('hg shelve [OPTION]... [FILE]...'))
 def shelvecmd(ui, repo, *pats, **opts):
     '''save and set aside changes from the working directory

tests/test-shelve.t

@@ -68,9 +68,12 b' shelve has a help message'
    -l --list                list current shelves
    -m --message TEXT        use text as shelve message
    -n --name NAME           use the given name for the shelved commit
-   -p --patch               show patch
+   -p --patch               output patches for changes (provide the names of the
+                            shelved changes as positional arguments)
    -i --interactive         interactive mode, only works while creating a shelve
-      --stat                output diffstat-style summary of changes
+      --stat                output diffstat-style summary of changes (provide
+                            the names of the shelved changes as positional
+                            arguments)
    -I --include PATTERN [+] include names matching the given patterns
    -X --exclude PATTERN [+] exclude names matching the given patterns
       --mq                  operate on patch repository