Tell the user the real "hg update -C" command, not just "-C" when aborting.

mercurial/localrepo.py

@@ -1662,7 +1662,7 b' class localrepository(object):'
                     self.ui.status(" %s%s\n" % (f, cf))
                 self.ui.warn(_("aborting update spanning branches!\n"))
                 self.ui.status(_("(use 'hg merge' to merge across branches"
-                                 " or '-C' to lose changes)\n"))
+                                 " or 'hg update -C' to lose changes)\n"))
                 return 1
             branch_merge = True
 

tests/test-merge5.out

@@ -2,4 +2,4 b' removing b'
 this update spans a branch affecting the following files:
  b
 aborting update spanning branches!
-(use 'hg merge' to merge across branches or '-C' to lose changes)
+(use 'hg merge' to merge across branches or 'hg update -C' to lose changes)

tests/test-up-local-change.out

@@ -101,7 +101,7 b' this update spans a branch affecting the'
  a (resolve)
  b (resolve)
 aborting update spanning branches!
-(use 'hg merge' to merge across branches or '-C' to lose changes)
+(use 'hg merge' to merge across branches or 'hg update -C' to lose changes)
 failed
 abort: outstanding uncommitted changes
 failed