purge: use opts.get()

Most commands use opts.get() to retrieve values for options
that may not be explicitly passed. purge wasn't.

This makes it easier to call purge() from 3rd party extensions.

hgext/purge.py

@@ -84,13 +84,13 b' def purge(ui, repo, *dirs, **opts):'
     list of files that this program would delete, use the --print
     option.
     '''
-    act = not opts['print']
+    act = not opts.get('print')
     eol = '\n'
-    if opts['print0']:
+    if opts.get('print0'):
         eol = '\0'
         act = False # --print0 implies --print
-    removefiles = opts['files']
-    removedirs = opts['dirs']
+    removefiles = opts.get('files')
+    removedirs = opts.get('dirs')
     if not removefiles and not removedirs:
         removefiles = True
         removedirs = True
@@ -101,7 +101,7 b' def purge(ui, repo, *dirs, **opts):'
                 remove_func(repo.wjoin(name))
             except OSError:
                 m = _('%s cannot be removed') % name
-                if opts['abort_on_err']:
+                if opts.get('abort_on_err'):
                     raise error.Abort(m)
                 ui.warn(_('warning: %s\n') % m)
         else:
@@ -111,7 +111,7 b' def purge(ui, repo, *dirs, **opts):'
     if removedirs:
         directories = []
         match.explicitdir = match.traversedir = directories.append
-    status = repo.status(match=match, ignored=opts['all'], unknown=True)
+    status = repo.status(match=match, ignored=opts.get('all'), unknown=True)
 
     if removefiles:
         for f in sorted(status.unknown + status.ignored):