Add libssh2's library and include directories.

Follow-up to 4f91bfa3 ("Find libssh2 via pkg-config"): FindPkgConfig sets
<foo>_INCLUDE_DIRS, not <foo>_INCLUDE_DIR like FindLIBSSH2 did.

Additionally, if using only FindPkgConfig to find libssh2, we have to
call LINK_DIRECTORIES() as well to pass the appropriate -L entries,
otherwise the build will only work if libssh2.so is in a directory
searched automatically by the linker.

CMakeLists.txt

@@ -217,7 +217,8 @@ IF (USE_SSH)
 ENDIF()
 IF (LIBSSH2_FOUND)
 	ADD_DEFINITIONS(-DGIT_SSH)
-	INCLUDE_DIRECTORIES(${LIBSSH2_INCLUDE_DIR})
+	INCLUDE_DIRECTORIES(${LIBSSH2_INCLUDE_DIRS})
+	LINK_DIRECTORIES(${LIBSSH2_LIBRARY_DIRS})
 	SET(LIBGIT2_PC_REQUIRES "${LIBGIT2_PC_REQUIRES} libssh2")
 	SET(SSH_LIBRARIES ${LIBSSH2_LIBRARIES})
 ENDIF()