revert: rewrite help summary

New users have a tendency to mistake 'revert' as the command to use to
check out old revisions. They also occasionally mistake revert for a
generalized undo (compare rollback).

This version intentionally aims to avoid mentioning 'earlier' and thus
intentionally no longer alludes to the (secondary) -r behavior (which
in fact is not actually limited to 'earlier').

Instead, we mention checkout state, to convey that we can
restore things to the way they were when checked out.

mercurial/commands.py

@@ -4086,7 +4086,7 b' def resolve(ui, repo, *pats, **opts):'
     ] + walkopts + dryrunopts,
     _('[OPTION]... [-r REV] [NAME]...'))
 def revert(ui, repo, *pats, **opts):
-    """restore individual files or directories to an earlier state
+    """restore files to their checkout state
 
     .. note::
        This command is most likely not what you are looking for.

tests/test-globalopts.t

@@ -316,7 +316,7 b' Testing -h/--help:'
    remove       remove the specified files on the next commit
    rename       rename files; equivalent of copy + remove
    resolve      redo merges or set/view the merge status of files
-   revert       restore individual files or directories to an earlier state
+   revert       restore files to their checkout state
    rollback     roll back the last transaction (dangerous)
    root         print the root (top) of the current working directory
    serve        start stand-alone webserver
@@ -396,7 +396,7 b' Testing -h/--help:'
    remove       remove the specified files on the next commit
    rename       rename files; equivalent of copy + remove
    resolve      redo merges or set/view the merge status of files
-   revert       restore individual files or directories to an earlier state
+   revert       restore files to their checkout state
    rollback     roll back the last transaction (dangerous)
    root         print the root (top) of the current working directory
    serve        start stand-alone webserver

tests/test-help.t

@@ -86,7 +86,7 b' Short help:'
    remove       remove the specified files on the next commit
    rename       rename files; equivalent of copy + remove
    resolve      redo merges or set/view the merge status of files
-   revert       restore individual files or directories to an earlier state
+   revert       restore files to their checkout state
    rollback     roll back the last transaction (dangerous)
    root         print the root (top) of the current working directory
    serve        start stand-alone webserver
@@ -160,7 +160,7 b' Short help:'
    remove       remove the specified files on the next commit
    rename       rename files; equivalent of copy + remove
    resolve      redo merges or set/view the merge status of files
-   revert       restore individual files or directories to an earlier state
+   revert       restore files to their checkout state
    rollback     roll back the last transaction (dangerous)
    root         print the root (top) of the current working directory
    serve        start stand-alone webserver
@@ -673,7 +673,7 b' Test that default list of commands omits'
    remove       remove the specified files on the next commit
    rename       rename files; equivalent of copy + remove
    resolve      redo merges or set/view the merge status of files
-   revert       restore individual files or directories to an earlier state
+   revert       restore files to their checkout state
    rollback     roll back the last transaction (dangerous)
    root         print the root (top) of the current working directory
    serve        start stand-alone webserver