[Xcconfig] Reference vendored libraries & frameworks with a relative path

Closes #1405

CHANGELOG.md

@@ -9,6 +9,12 @@ To install or update CocoaPods see this [guide](http://docs.cocoapods.org/guides
 * The Pods project now is sorted by name.  
   [#1389](https://github.com/CocoaPods/CocoaPods/pull/1389)
 
+###### Bug Fixes
+
+* The search paths of vendored frameworks and libraries now are always
+  specified relatively.  
+  [#1405](https://github.com/CocoaPods/CocoaPods/pull/1405)
+
 
 ## 0.25.0
 [CocoaPods](https://github.com/CocoaPods/CocoaPods/compare/0.24.0...0.25.0)

lib/cocoapods/generator/xcconfig/xcconfig_helper.rb

@@ -60,7 +60,7 @@ module Pod
         #
         def self.add_framework_build_settings(framework_path, xcconfig, sandbox_root)
           name = File.basename(framework_path, ".framework")
-          dirname = File.dirname(framework_path).sub(sandbox_root.to_s, '$(PODS_ROOT)')
+          dirname = '$(PODS_ROOT)/' + framework_path.dirname.relative_path_from(sandbox_root).to_s
           build_settings = {
             'OTHER_LDFLAGS' => "-framework #{name}",
             'FRAMEWORK_SEARCH_PATHS' => quote([dirname])
@@ -79,7 +79,7 @@ module Pod
         #
         def self.add_library_build_settings(library_path, xcconfig, sandbox_root)
           name = File.basename(library_path, ".a").sub(/\Alib/, '')
-          dirname = File.dirname(library_path).sub(sandbox_root.to_s, '$(PODS_ROOT)')
+          dirname = '$(PODS_ROOT)/' + library_path.dirname.relative_path_from(sandbox_root).to_s
           build_settings = {
             'OTHER_LDFLAGS' => "-l#{name}",
             'LIBRARY_SEARCH_PATHS' => quote([dirname])