Add standard package paths to allow for extension mechanism

src/_premake_main.lua

@@ -35,6 +35,16 @@
 
 		_PREMAKE_COMMAND = path.getabsolute(_PREMAKE_COMMAND)
 
+        -- Enable extensions - the '?' character is replaced with the extension
+        -- name so the extension directory name _must_ be the same as the
+        -- extension Lua file.  eg. .../d/d.lua, .../codelite/codelite.lua etc
+        local extdirs = { 
+            path.getdirectory( _PREMAKE_COMMAND ) .. "/ext/?/?.lua", 
+            "./premake/?/?.lua", 
+            "/usr/share/premake/?/?.lua" }
+        for _,v in ipairs(extdirs) do
+            package.path = package.path .. ";" .. v
+        end
 
 		-- The "next-gen" actions have now replaced their deprecated counterparts.
 		-- Provide a warning for a little while before I remove them entirely.