* improved documentation of the default destination on the download
cache and the concomitant consequences
* removed NETWORK_WIMAX flag for setting allowed networks
* changed request headers behavior to support multiple instances of
the same header (as allowed in the HTTP spec), renamed
setRequestHeader() to addRequestHeader()
* accept user-facing strings as CharSequences instead of Strings
* new convenience methods setDestinationInExternalFilesDir() and
setDestinationInExternalPublicDir() for setting a destination in
either shared or app-private external storage directories
* renamed setMediaType() to setMimeType()
Change-Id: I8781e2214d939c340209cab917bbbba264ab919c
4f564cdeb8