releasenotes: make the import of fuzzywuzzy optional

If fuzzywuzzy is note present, we will not be having the capability to merge
existing releasenotes with the new releasenotes on the similarity basis.
The merging will still work good for exact same releasenotes entries.

Differential Revision: https://phab.mercurial-scm.org/D1096

hgext/releasenotes.py

@@ -218,7 +218,12 b' def similaritycheck(incoming_str, existi'
     """
     Returns false when note fragment can be merged to existing notes.
     """
-    import fuzzywuzzy.fuzz as fuzz
+    try:
+        import fuzzywuzzy.fuzz as fuzz
+        fuzz.token_set_ratio
+    except ImportError:
+        return True
+
     merge = True
     for bullet in existingnotes:
         score = fuzz.token_set_ratio(incoming_str, bullet)