FindProtobuf: fix protobuf_generate_*() to handle proto files in subdirs.

Modules/FindProtobuf.cmake

@@ -144,6 +144,10 @@ function(PROTOBUF_GENERATE_CPP SRCS HDRS)
   foreach(FIL ${ARGN})
     get_filename_component(ABS_FIL ${FIL} ABSOLUTE)
     get_filename_component(FIL_WE ${FIL} NAME_WE)
+    get_filename_component(FIL_DIR ${FIL} DIRECTORY)
+    if(FIL_DIR)
+      set(FIL_WE "${FIL_DIR}/${FIL_WE}")
+    endif()
 
     list(APPEND ${SRCS} "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}.pb.cc")
     list(APPEND ${HDRS} "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}.pb.h")
@@ -197,6 +201,10 @@ function(PROTOBUF_GENERATE_PYTHON SRCS)
   foreach(FIL ${ARGN})
     get_filename_component(ABS_FIL ${FIL} ABSOLUTE)
     get_filename_component(FIL_WE ${FIL} NAME_WE)
+    get_filename_component(FIL_DIR ${FIL} DIRECTORY)
+    if(FIL_DIR)
+      set(FIL_WE "${FIL_DIR}/${FIL_WE}")
+    endif()
 
     list(APPEND ${SRCS} "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}_pb2.py")
     add_custom_command(