build: Check for pod2man instead of perl for manual page generation

Some systems provide Perl without pod2man.

configure

@@ -1124,7 +1124,7 @@ CONFIG_LIST="
     memalign_hack
     network
     nonfree
-    perl
+    pod2man
     pic
     rdft
     runtime_cpudetect
@@ -1974,7 +1974,7 @@ avserver_select="ffm_muxer rtp_protocol rtsp_demuxer"
 avserver_extralibs='$ldl'
 
 # documentation
-perl_deps="doc"
+pod2man_deps="doc"
 texi2html_deps="doc"
 
 # default parameters
@@ -3881,7 +3881,7 @@ if check_pkg_config sdl SDL_events.h SDL_PollEvent; then
     enable sdl
 fi
 
-perl -v            > /dev/null 2>&1 && enable perl      || disable perl
+pod2man --help     > /dev/null 2>&1 && enable pod2man   || disable pod2man
 texi2html -version > /dev/null 2>&1 && enable texi2html || disable texi2html
 
 check_header linux/fb.h

doc/Makefile

@@ -11,7 +11,7 @@ HTMLPAGES   = $(AVPROGS-yes:%=doc/%.html)                               \
               doc/nut.html                                              \
               doc/platform.html                                         \
 
-DOCS-$(CONFIG_PERL)                             += $(MANPAGES) $(PODPAGES)
+DOCS-$(CONFIG_POD2MAN)                          += $(MANPAGES) $(PODPAGES)
 DOCS-$(CONFIG_TEXI2HTML)                        += $(HTMLPAGES)
 DOCS = $(DOCS-yes)
 
@@ -59,7 +59,7 @@ OBJDIRS += doc/examples
 doc/doxy/html: $(SRC_PATH)/doc/Doxyfile $(INSTHEADERS)
 	$(M)$(SRC_PATH)/doc/doxy-wrapper.sh $(SRC_PATH) $^
 
-install-progs-$(CONFIG_PERL): install-man
+install-progs-$(CONFIG_POD2MAN): install-man
 install-progs-$(CONFIG_TEXI2HTML): install-doc
 
 install-doc: $(HTMLPAGES)