Improved sanitizing of configuration names which have a number prefix.

lib/cocoapods/project.rb

@@ -209,7 +209,7 @@ module Pod
     #
     def add_build_configuration(name, type)
       build_configuration = super
-      values = ["#{name.gsub(/[^a-zA-Z0-9_]/, '_').upcase}=1"]
+      values = ["#{name.gsub(/[^a-zA-Z0-9_]/, '_').gsub(/(^[0-9])/, '_\1').upcase}=1"]
       settings = build_configuration.build_settings
       definitions = Array(settings['GCC_PREPROCESSOR_DEFINITIONS'])
       values.each do |value|

spec/unit/project_spec.rb

@@ -234,9 +234,9 @@ module Pod
         end
 
         it "doesn't create invalid preprocessor definitions for configurations" do
-          configuration = @project.add_build_configuration('Release-Foo.bar', :release)
+          configuration = @project.add_build_configuration('1 Release-Foo.bar', :release)
           settings = configuration.build_settings
-          settings['GCC_PREPROCESSOR_DEFINITIONS'].should.include('RELEASE_FOO_BAR=1')
+          settings['GCC_PREPROCESSOR_DEFINITIONS'].should.include('_1_RELEASE_FOO_BAR=1')
         end
 
         it "doesn't duplicate values" do