Fix problem with .options file and extension fields.

The options for an extension field were being looked up under wrong name
(MessageName instead of MessageName.fieldname).

Fixed the problem and added regression test. Created a new subfolder for
regression test cases.

Update issue 125
Status: FixedInGit

tests/regression/issue_125/SConscript

@@ -0,0 +1,9 @@
+# Regression test for Issue 125: Wrong identifier name for extension fields
+
+Import("env")
+
+env.NanopbProto(["extensionbug", "extensionbug.options"])
+env.Object('extensionbug.pb.c')
+
+env.Match(['extensionbug.pb.h', 'extensionbug.expected'])
+