programmer.txt has now priority over platforms.txt tools definitions

This allows properties defined in programmers.txt to override generic
configurations in platform.txt where needed, for example in the
following configuration:

programmers.txt:

   myprog.name=My New Programmer
   [...]
   myprog.program.tool=avrdude
   myprog.config.path={runtime.platform.path}/myprog_avrdude.conf
   [...]

platform.txt:

   tools.avrdude.path={runtime.tools.avrdude.path}
   tools.avrdude.cmd.path={path}/bin/avrdude
   tools.avrdude.config.path={path}/etc/avrdude.conf
   [...]
   tools.avrdude.upload.pattern="{cmd.path}" "-C{config.path}" {upload.verbose} -p{build.mcu} -c{upload.protocol} -P{serial.port} -b{upload.speed} -D "-Uflash:w:{build.path}/{build.project_name}.hex:i"

the generic tools.avrdude.config.path value

   {path}/etc/avrdude.conf

is replaced by the more specific myprog.config.path used in "myprog" programmer

   {runtime.plaform.path}/myprog_avrdude.conf

arduino-core/src/cc/arduino/packages/uploaders/SerialUploader.java

@@ -253,8 +253,8 @@ public boolean uploadUsingProgrammer(String buildPath, String className) throws
     if (programmerPrefs == null)
       throw new RunnerException(
           _("Please select a programmer from Tools->Programmer menu"));
+    prefs.putAll(targetPlatform.getTool(programmerPrefs.getOrExcept("program.tool")));
     prefs.putAll(programmerPrefs);
-    prefs.putAll(targetPlatform.getTool(prefs.getOrExcept("program.tool")));
 
     prefs.put("build.path", buildPath);
     prefs.put("build.project_name", className);