Make locations overridables. (Passed as MAKE_ARGS.)

--- Makefile.config.orig	2018-07-24 11:34:38 UTC
+++ Makefile.config
@@ -17,62 +17,62 @@
 #
 # the base of the Munin installation.
 #
-PREFIX     = $(DESTDIR)/opt/munin
+PREFIX     ?= $(DESTDIR)/opt/munin
 
 # Where Munin keeps its configurations (server.conf, client.conf, ++)
-CONFDIR    = $(DESTDIR)/etc/opt/munin
+CONFDIR    ?= $(DESTDIR)/etc/opt/munin
 
 # Server only - where to put munin-cron
-BINDIR     = $(PREFIX)/bin
+BINDIR     ?= $(PREFIX)/bin
 
 # Client only - where to put munin-node, munin-node-configure, and munin-run
-SBINDIR    = $(PREFIX)/sbin
+SBINDIR    ?= $(PREFIX)/sbin
 
 # Where to put text and html documentation
-DOCDIR     = $(PREFIX)/doc
+DOCDIR     ?= $(PREFIX)/doc
 
 # Where to put man pages
-MANDIR     = $(PREFIX)/man
+MANDIR     ?= $(PREFIX)/man
 
 # Where to put internal binaries and plugin repository
-LIBDIR     = $(PREFIX)/lib
+LIBDIR     ?= $(PREFIX)/lib
 
 # Server only - Output directory
-HTMLDIR    = $(PREFIX)/www/docs
-CGIDIR     = $(PREFIX)/www/cgi
+HTMLDIR    ?= $(PREFIX)/www/docs
+CGIDIR     ?= $(PREFIX)/www/cgi
 
 # Where to put internal data for master (RRD, internal files, ...)
-DBDIR      = $(DESTDIR)/var/opt/munin
+DBDIR      ?= $(DESTDIR)/var/opt/munin
 
 # Where to put internal data for node (plugin state, ...)
-DBDIRNODE  = $(DESTDIR)/var/opt/munin-node
+DBDIRNODE  ?= $(DESTDIR)/var/opt/munin-node
 
 # Client only - Where the spool files are written. Must be writable by
 # group "munin", and should be preserved between reboots
-SPOOLDIR   = $(DBDIR)/spool
+SPOOLDIR   ?= $(DBDIR)/spool
 
 # Client only - Where plugins should put their states. Must be writable by
 # group "munin", and should be preserved between reboots
-PLUGSTATE  = $(DBDIRNODE)/plugin-state
+PLUGSTATE  ?= $(DBDIRNODE)/plugin-state
 
 # Where Munin should place its logs.
-LOGDIR     = $(PREFIX)/log/munin
+LOGDIR     ?= $(PREFIX)/log/munin
 
 # Location of PID files and other statefiles. On the server, must be
 # writable by the user "munin".
-STATEDIR   = $(DESTDIR)/var/run/munin
+STATEDIR   ?= $(DESTDIR)/var/run/munin
 
 # The perl interpreter to use
-PERL       := $(shell which perl)
+PERL       := /usr/local/bin/perl
 
 # The python interpreter to use (used by some plugins)
-PYTHON     := /usr/bin/env python3
+PYTHON     := /usr/local/bin/python
 
 # The ruby interpreter to use (used by some plugins)
-RUBY       := /usr/bin/env ruby
+RUBY       := /usr/local/bin/ruby
 
 # The java runtime to use (used by some plugins)
-JAVARUN    := /usr/bin/java
+JAVARUN    := /usr/local/bin/java
 
 # The java library dir to use (used by some plugins)
 # this is needed in order to be able to install
@@ -92,7 +92,7 @@ JAVALIBDIR = $(LIBDIR)
 GOODSH     := $(shell PATH=`getconf PATH 2>/dev/null || echo $(PATH)` LANG=C sh -c 'type sh | sed "s/.* //"')
 
 # Path of bash for bash specific plugins
-BASH       := /bin/bash
+BASH       := /usr/local/bin/bash
 
 # Server only - Where to install the perl libraries
 PERLLIB    = $(DESTDIR)$(shell $(PERL) -V:sitelib | cut -d"'" -f2)