don't assume grid is regular in addcyclic

Author: Jeff Whitaker

Changelog

@@ -1,5 +1,8 @@
 version 1.0.8 (not yet released)
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+* don't assume grid is regular with adding cyclic point in addcyclic. 
+  New kwarg 'cyclic_dimension' added, with a default of 360.  Partially
+  addresses issue 139.
 * fix for coastline drawing glitch (issue 123).
 * update shapefile.py to version 1.2.0 from pyshp.googlecode.com. Add back
   in modification clobbered in upgrade to version 1.1.7 (issue 30).