Fix up handing of fields with leading names that should be all caps.

Add a compile test to confirm things are working as expected.
diff --git a/Makefile.am b/Makefile.am
index 3e21db8..064efdf 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -413,6 +413,7 @@
   objectivec/GPBCodedInputStream_PackagePrivate.h                            \
   objectivec/GPBCodedOutputStream.h                                          \
   objectivec/GPBCodedOutputStream.m                                          \
+  objectivec/GPBCodedOutputStream_PackagePrivate.h                           \
   objectivec/GPBDescriptor.h                                                 \
   objectivec/GPBDescriptor.m                                                 \
   objectivec/GPBDescriptor_PackagePrivate.h                                  \