ignore: move bad file handling out of readignorefile

ignore: move bad file handling out of readignorefile

In preparation for moving readignorefile to match.py to make it more generally
usable, let's move the bad ignore file handling up to the ignore specific logic.

--- a/mercurial/ignore.py	Sat May 16 15:24:43 2015 -0700
+++ b/mercurial/ignore.py	Sat May 16 15:37:59 2015 -0700
@@ -56,16 +56,11 @@
     return patterns, warnings
 
 def readignorefile(filepath, warn):
-    try:
-        pats = []
-        fp = open(filepath)
-        pats, warnings = ignorepats(fp)
-        fp.close()
-        for warning in warnings:
-            warn("%s: %s\n" % (filepath, warning))
-    except IOError, inst:
-        warn(_("skipping unreadable ignore file '%s': %s\n") %
-             (filepath, inst.strerror))
+    fp = open(filepath)
+    pats, warnings = ignorepats(fp)
+    fp.close()
+    for warning in warnings:
+        warn("%s: %s\n" % (filepath, warning))
     return pats
 
 def readpats(root, files, warn):
@@ -75,7 +70,11 @@
     for f in files:
         if f in pats:
             continue
-        pats[f] = readignorefile(f, warn)
+        try:
+            pats[f] = readignorefile(f, warn)
+        except IOError, inst:
+            warn(_("skipping unreadable ignore file '%s': %s\n") %
+                 (f, inst.strerror))
 
     return [(f, pats[f]) for f in files if f in pats]