fileset: use filectx.isbinary() to filter out binaries in eol()

Since LFS stores the binary attribute in the pointer file, this means that the
file doesn't need to be downloaded in order to be skipped.  This function also
catches an IOError if the data can't be loaded in the non-LFS case.

I wonder if it's worth storing the unix/dos attributes in the pointer file as
well, though I'd expect LFS files to be binary most of the time.

mercurial/fileset.py

@@ -448,9 +448,10 b' def eol(mctx, x):'
 
     s = []
     for f in mctx.existing():
-        d = mctx.ctx[f].data()
-        if stringutil.binary(d):
+        fctx = mctx.ctx[f]
+        if fctx.isbinary():
             continue
+        d = fctx.data()
         if (enc == 'dos' or enc == 'win') and '\r\n' in d:
             s.append(f)
         elif enc == 'unix' and re.search('(?<!\r)\n', d):

tests/test-lfs.t

@@ -515,6 +515,17 b' enabled adds the lfs requirement'
   d: binary=False
   b55353847f02 tip
 
+Binary blobs don't need to be present to be skipped in filesets.  (And their
+absence doesn't cause an abort.)
+
+  $ rm .hg/store/lfs/objects/96/a296d224f285c67bee93c30f8a309157f0daa35dc5b87e410b78630a09cfc7
+  $ rm .hg/store/lfs/objects/92/f76135a4baf4faccb8586a60faf830c2bdfce147cefa188aaf4b790bd01b7e
+
+  $ hg files --debug -r . 'set:eol("unix")' --config 'experimental.lfs.disableusercache=True'
+  lfs: found c04b5bb1a5b2eb3e9cd4805420dba5a9d133da5b7adeeafb5474c4adae9faa80 in the local lfs store
+  lfs: found 5dde896887f6754c9b15bfe3a441ae4806df2fde94001311e08bf110622e0bbe in the local lfs store
+           2   b
+
   $ cd ..
 
 # Test fctx.cmp fastpath - diff without LFS blobs