Allow the possibilioty to use custom makefile

user can now include Makefile in another file to set custom values for these parameters:

* OSM_PREFIX
* OSM_NAME_COLUMN
* OSM_SRID
* OSM_UNITS
* OSM_DB_CONNECTION
* OSM_EXTENT
* OSM_WMS_SRS
* STYLE
* DEBUG
* LAYERDEBUG

Makefile

@@ -10,19 +10,19 @@ CPP=gcc -E -x c
 #if the preprocessor fails for some reason, try replacing this with "cpp" on linux, or "cpp-4.2" on darwin (not available starting with mountain lion)
 
 
-OSM_PREFIX=osm_new_
-OSM_NAME_COLUMN=name
-OSM_SRID=4326
-OSM_UNITS=dd
-OSM_EXTENT=-180 -90 180 90
-OSM_SRID=3857
-OSM_UNITS=meters
-OSM_DB_CONNECTION=host=localhost dbname=osm user=osm password=osm port=5432
+OSM_PREFIX?=osm_new_
+OSM_NAME_COLUMN?=name
+#OSM_SRID?=4326
+#OSM_UNITS?=dd
+#OSM_EXTENT?=-180 -90 180 90
+OSM_SRID?=3857
+OSM_UNITS?=meters
+OSM_DB_CONNECTION?=host=localhost dbname=osm user=osm password=osm port=5432
 OSM_EXTENT=-20000000 -20000000 20000000 20000000
-OSM_WMS_SRS=EPSG:900913 EPSG:4326 EPSG:3857 EPSG:2154 EPSG:310642901 EPSG:4171 EPSG:310024802 EPSG:310915814 EPSG:310486805 EPSG:310702807 EPSG:310700806 EPSG:310547809 EPSG:310706808 EPSG:310642810 EPSG:310642801 EPSG:310642812 EPSG:310032811 EPSG:310642813 EPSG:2986
-DEBUG=1
-LAYERDEBUG=1
-STYLE=default
+OSM_WMS_SRS?=EPSG:900913 EPSG:4326 EPSG:3857 EPSG:2154 EPSG:310642901 EPSG:4171 EPSG:310024802 EPSG:310915814 EPSG:310486805 EPSG:310702807 EPSG:310700806 EPSG:310547809 EPSG:310706808 EPSG:310642810 EPSG:310642801 EPSG:310642812 EPSG:310032811 EPSG:310642813 EPSG:2986
+DEBUG?=1
+LAYERDEBUG?=1
+STYLE?=default
 #can also use google or bing
 
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