largefiles: don't mangle filesets when fixing up the log matcher

The fileset-generated.t test previously failed with this:

  +  hg: parse error: unknown identifier: .hglf/modified
  +  (did you mean 'modified'?)
  +  [255]

Filesets will find the standins on their own, without any help.  While that's
useful for some things like modified(), clean(), etc., it is wrong for things
like size().  Proper fileset support for largefiles is not trivial, but this was
failing with just the extension enabled on a normal repo.

hgext/largefiles/overrides.py

@@ -305,6 +305,9 b' def overridelog(orig, ui, repo, *pats, *'
         pats = set(p)
 
         def fixpats(pat, tostandin=lfutil.standin):
+            if pat.startswith('set:'):
+                return pat
+
             kindpat = match_._patsplit(pat, None)
 
             if kindpat[0] is not None:

tests/test-fileset-generated.t

@@ -72,6 +72,20 b' Test log'
    content1_content2_content3-tracked |  1 +
    3 files changed, 3 insertions(+), 0 deletions(-)
   
+Largefiles doesn't crash
+  $ hg log -T '{rev}\n' --stat 'set:modified()' --config extensions.largefiles=
+  1
+   content1_content2_content1-tracked |  2 +-
+   content1_content2_content3-tracked |  2 +-
+   missing_content2_content3-tracked  |  1 +
+   3 files changed, 3 insertions(+), 2 deletions(-)
+  
+  0
+   content1_content1_content3-tracked |  1 +
+   content1_content2_content1-tracked |  1 +
+   content1_content2_content3-tracked |  1 +
+   3 files changed, 3 insertions(+), 0 deletions(-)
+  
   $ hg log -T '{rev}\n' --stat 'set:added()'
   1
    content1_missing_content1-tracked |  1 -

tests/test-largefiles-misc.t

@@ -37,6 +37,13 b' Test copies and moves from a directory o'
   A dira/dirb/largefile
   $ cd dira
   $ hg cp dirb/largefile foo/largefile
+
+TODO: Ideally, this should mention the largefile, not the standin
+  $ hg log -T '{rev}\n' --stat 'set:clean()'
+  0
+   .hglf/dira/dirb/largefile |  1 +
+   1 files changed, 1 insertions(+), 0 deletions(-)
+  
   $ hg ci -m "deep copy"
   Invoking status precommit hook
   A dira/foo/largefile