Fix and clean up some comments

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>

include/empthread.h

@@ -55,7 +55,7 @@
 
 /* Abstract data types */
 
-/* A thread.  */
+/* A thread. */
 typedef struct lwpProc empth_t;
 
 /* A read-write lock, perferring writers */

include/nat.h

@@ -135,8 +135,8 @@ struct natstr {
 
 /*
  * Number of updates contact lasts for various ways of making contact.
- * These are only useful with option LOSE_CONTACT option, which
- * implies option HIDDEN.
+ * These are only useful with option LOSE_CONTACT, which implies
+ * option HIDDEN.
  */
 /* Planes spotting and being spotted */
 #define FOUND_FLY	3

include/nsc.h

@@ -63,10 +63,10 @@ enum nsc_type {
     NSC_NATID = NSC_UCHAR	/* nation id */
 };
 
-/* Is TYPE a promoted value type?  */
+/* Is TYPE a promoted value type? */
 #define NSC_IS_PROMOTED(type) (NSC_LONG <= (type) && (type) <= NSC_STRING)
 
-/* Return nsc_type for a signed integer with the same size as TYPE.  */
+/* Return nsc_type for a signed integer with the same size as TYPE. */
 #define NSC_SITYPE(type)				\
     (sizeof(type) == 1 ? NSC_CHAR			\
      : sizeof(type) == sizeof(short) ? NSC_SHORT	\