google-talk-plugin: Update to 5.1.5.0

(cherry picked from commit 34874dac7a7dc4ba3c552bbcda38a0434c1f5d8c)
nixUnstable: Update to 1.7pre3520_1017bd6

(cherry picked from commit 19350fac6606e15e57650622e0f7092dbb398a19)