THRIFT-2651: struct names that are restricted erlang terms generate invalid type signatures

patch: alisdairsullivan@yahoo.ca
client: erlang

fixes error exposed in THRIFT-2647 by avoiding using restricted identifiers in erlang type signatures generated by the compiler
diff --git a/test/NameConflictTest.thrift b/test/NameConflictTest.thrift
index ad333eb..4960f54 100644
--- a/test/NameConflictTest.thrift
+++ b/test/NameConflictTest.thrift
@@ -41,6 +41,10 @@
   2: string where
 }
 
+struct ofOf {
+  1: of Of
+}
+
 
 struct ClassAndProp {
   1: bool ClassAndProp