Rename documentation source files to avoid filesystem case and restricted

filename issues when checking out the source on other operating systems.

I've verified the generated paper.ascii is identical before and after the
change.

share/doc/psd/15.yacc/Makefile

@@ -2,8 +2,8 @@
 # $FreeBSD$
 
 VOLUME=		psd/15.yacc
-SRCS=		stubs ss.. ss0 ss1 ss2 ss3 ss4 ss5 ss6 ss7 ss8 ss9 \
-		ssA ssB ssa ssb ssc ssd
+SRCS=		stubs ss_ ss0 ss1 ss2 ss3 ss4 ss5 ss6 ss7 ss8 ss9 \
+		ss10 ss11 ssa ssb ssc ssd
 EXTRA=		ref.bib
 MACROS=		-ms
 USE_REFER=