New report field: 'STACK_TRACE_HASH'.
This field contains a hash of the reported stacktrace, facilitating grouping of similar crashes.
As discussed here: https://groups.google.com/forum/#!searchin/acra-discuss/bod/acra-discuss/DajoZbpO-4w/Fvd1LVx_09sJ
Remerge of pull request 141 - Configuring a different SocketFactory for HTTPs.
Prevent potential race-condition when sending reports at startup

In theory, the SendWorker() can start sending reports before
mReportSenders has been properly set. This is extremely unlikely
in practice due to the overhead of spawning a new thread and the
amount of code that is executed by the SendWorker before it needs
to access mReportSenders.

But we can prevent the race from occuring in theory as well as in
practice by deferring calling checkReportsOnApplicationStart()
till after mReportSenders has been set.

https://github.com/ACRA/acra/issues/200
Don't spawn thread to wait for SendWorker on handleSilentException()

Small optmization, but there's no reason to spawn a thread to wait
around on the SendWorker when invoked via handleSilentException(),
since there's otherwise nothing for that thread to do.
Merge pull request #201 from jaysoffian/prevent_startup_race

Prevent potential race-condition when sending reports at startup
Small cleanup for PR#202 Don't spawn thread to wait for SendWorker on handleSilentException().
Renamed forceSilentReport param for better comprehension.
Merge branch 'master' of github.com:ACRA/acra
Merge pull request #170 from william-ferguson-au/custom-https-socket-2

Remerge of pull request 141 - Configuring a different SocketFactory for HTTPs.
Merged PR#89 branch 'feature_stackTraceHash' of https://github.com/BoD/acra into merging_89
Removed unused import.
Removed GoogleFormSender - it has been obsolete for more than 2 years.