Dialyzer fixes

Add a new yaws_dynopts.erl warning to known_dialyzer_warnings. This
change allows dialyzer checking to pass on OTP 25.

If dialyzer emits warnings, it exits with status 2, which causes make
to fail. Since warnings can often be inconsequential, modify the make
yaws.plt rule to change exit status 2 to 0 so that make passes even if
warnings occur.

Makefile.am

@@ -96,6 +96,9 @@ list-checks:
 cleantest:
 	$(AM_V_at)( cd test && $(MAKE) clean )
 
+# If dialyzer exits with status 2, it means it emitted warnings. In
+# that case, exit with status 0 instead of failing the build, since
+# warnings are typically inconsequential.
 yaws.plt:
 	$(AM_V_GEN)$(DIALYZER) --build_plt -r ebin --output_plt yaws.plt\
 	  -r $(ERLANG_LIB_DIR_kernel) 					\
@@ -109,7 +112,8 @@ yaws.plt:
 	  -r $$(echo $(ERLANG_LIB_DIR_mnesia) | sed "s/not found//")	\
 	  -r $$(echo $(ERLANG_LIB_DIR_inets)  | sed "s/not found//")	\
 	  -r $$(echo $(ERLANG_LIB_DIR_xmlrpc) | sed "s/not found//")	\
-	  -r $$(echo $(ERLANG_LIB_DIR_erlsom) | sed "s/not found//")
+	  -r $$(echo $(ERLANG_LIB_DIR_erlsom) | sed "s/not found//") ;  \
+	[ $$? -eq 2 ] && exit 0 || exit $$?
 
 dialyzer: all yaws.plt
 	$(AM_V_at)$(DIALYZER) -q --plt yaws.plt -r ebin | \

known_dialyzer_warnings

@@ -11,4 +11,5 @@ yaws_ctl.erl:\d+(:\d+)?: Function trace/1 has no local return
 yaws_ctl.erl:\d+(:\d+)?: Function debug_dump/1 has no local return
 yaws_ctl.erl:\d+(:\d+)?: Function stats/1 has no local return
 yaws_ctl.erl:\d+(:\d+)?: Function running_config/1 has no local return
+yaws_dynopts.erl:\d+(:\d+)?: The pattern 'true' can never match the type 'false'
 yaws_revproxy.erl:\d+(:\d+)?: The pattern 'true' can never match the type 'false'