devcam: add the -wipecache option

Change-Id: Ia3149361b3b210fd8e3b5fe42147018d3ab4e6fd
Option to restrict WiFI SSID for Android client

This is a first shot at
https://code.google.com/p/camlistore/issues/detail?id=496.

A user can enter a SSID and the upload will only run over Wifis with
this SSID. If the SSID option is left empty, everything works as before.

Change-Id: Ief3642c5b9c14d059f42696531fa33d1d780ab1c
Merge "Option to restrict WiFI SSID for Android client"
Use the 'purego' build tag, for cznic/zappy.

Change-Id: I23ef7e3f269fd884f77e61276468e023697d4580
Merge "devcam: add the -wipecache option"
Merge branch 'master' of https://camlistore.googlesource.com/camlistore