Add -keywords option to all FLAGS variables in make/docs/Makefile
as shown below. This adds HTML keywords for easier searching.

JAVADOCFLAGS
DOMAPI_JAVADOCFLAGS
DOCLETAPI_JAVADOCFLAGS
TAGLETAPI_JAVADOCFLAGS
JPEG_JAVADOCFLAGS
JDI_JAVADOCFLAGS
JAAS_JAVADOCFLAGS
JGSS_JAVADOCFLAGS