Created include/Makefile.in to separate header file installation from
the top-level Makefile.

diff --git a/configure.in b/configure.in
index b54f898..3705dc7 100644
--- a/configure.in
+++ b/configure.in
@@ -622,6 +622,7 @@
 graphics/win16drv/Makefile
 graphics/x11drv/Makefile
 if1632/Makefile
+include/Makefile
 ipc/Makefile
 library/Makefile
 libtest/Makefile