Create HTML manual at 'make dist' time

Per the suggestion of Greg Troxel, N1DAM, remove the need for the 'makeinfo'
dependency at build time by creating the HTML version of the manual along with
the info version at 'make dist' time.  The removes the build dependency on
'makeinfo' that was introduced since the release of 3.1.

(cherry picked from commit 6efb7b64b2)

doc/Makefile.am

@@ -2,7 +2,7 @@ EXTRA_DIST = hamlib.cfg index.doxygen hamlib.css footer.html \
 	Hamlib_design.eps Hamlib_design.png
 
 htmldir = $(docdir)/html
-html_DATA = Hamlib_design.png hamlib.html
+dist_html_DATA = Hamlib_design.png hamlib.html
 
 SRCDOCLST = ../src/rig.c ../src/rotator.c ../src/tones.c ../src/locator.c \
 		../src/event.c ../src/conf.c ../src/mem.c ../src/settings.c