ignore: remove .hgignore from ignore list if nonexistent

Previously we would always pass the root .hgignore path to the ignore parser.
The parser then had to be aware that the first path was special, and not warn if
it didn't exist.

In preparation for making the ignore file parser more generically usable, let's
make the parse logic not aware of this special case, and instead just not pass
the root .hgignore in if it doesn't exist.

mercurial/dirstate.py

@@ -143,7 +143,9 b' class dirstate(object):'
 
     @rootcache('.hgignore')
     def _ignore(self):
-        files = [self._join('.hgignore')]
+        files = []
+        if os.path.exists(self._join('.hgignore')):
+            files.append(self._join('.hgignore'))
         for name, path in self._ui.configitems("ui"):
             if name == 'ignore' or name.startswith('ignore.'):
                 # we need to use os.path.join here rather than self._join

mercurial/ignore.py

@@ -55,7 +55,7 b' def ignorepats(lines):'
 
     return patterns, warnings
 
-def readignorefile(filepath, warn, skipwarning=False):
+def readignorefile(filepath, warn):
     try:
         pats = []
         fp = open(filepath)
@@ -64,7 +64,6 b' def readignorefile(filepath, warn, skipw'
         for warning in warnings:
             warn("%s: %s\n" % (filepath, warning))
     except IOError, inst:
-        if not skipwarning:
             warn(_("skipping unreadable ignore file '%s': %s\n") %
                  (filepath, inst.strerror))
     return pats
@@ -76,8 +75,7 b' def readpats(root, files, warn):'
     for f in files:
         if f in pats:
             continue
-        skipwarning = f == files[0]
-        pats[f] = readignorefile(f, warn, skipwarning=skipwarning)
+        pats[f] = readignorefile(f, warn)
 
     return [(f, pats[f]) for f in files if f in pats]