added perf test for gpu::erode, fixed docs, refactored perf. sample

doc/gpu_initialization.tex

@@ -113,7 +113,7 @@ Returns true if the device has the given GPU feature, otherwise false.
 
 \cvdefCpp{bool DeviceInfo::has(GpuFeature feature);}
 \begin{description}
-\cvarg{feature}{Feature to be checked. See \hyperref[cpp.gpu.GpuFeature]{gpu::GpuFeature}.}
+\cvarg{feature}{Feature to be checked. See \hyperref[cpp.gpu.GpuFeature]{cv::gpu::GpuFeature}.}
 \end{description}
 
 
@@ -131,7 +131,7 @@ This class provides functionality (as set of static methods) for checking which
 The following method checks whether the module was built with the support of the given feature:
 \cvdefCpp{static bool builtWith(GpuFeature feature);}
 \begin{description}
-\cvarg{feature}{Feature to be checked. See \hyperref[cpp.gpu.GpuFeature]{gpu::GpuFeature}.}
+\cvarg{feature}{Feature to be checked. See \hyperref[cpp.gpu.GpuFeature]{cv::gpu::GpuFeature}.}
 \end{description}
 
 There are a set of methods for checking whether the module contains intermediate (PTX) or binary GPU code for the given architecture(s):