coverage: deal with symlinked input paths (MacOSX issue)

/tmp is symlinked in MacOSX therefore test scripts as well as python modules
are installed in a symlinked location. coverage.py uses abspath() to normalize
its inputs which fails if these are referencing real paths. Use realpath()
instead.

tests/coverage.py

@@ -412,6 +412,9 b' class coverage:'
         else:
             omit = []
 
+        omit = [os.path.normcase(os.path.abspath(os.path.realpath(p)))
+                for p in omit]
+
         if settings.get('report'):
             self.report(args, show_missing, ignore_errors, omit_prefixes=omit)
         if settings.get('annotate'):
@@ -537,7 +540,7 b' class coverage:'
                     if os.path.exists(g):
                         f = g
                         break
-            cf = os.path.normcase(os.path.abspath(f))
+            cf = os.path.normcase(os.path.abspath(os.path.realpath(f)))
             self.canonical_filename_cache[filename] = cf
         return self.canonical_filename_cache[filename]