Add option to do decryption synchronously
* src/common_indep.h (syncDec): New option. * src/main.c (read_options): Read it. * src/mail.cpp (do_parsing): Do not use windowmessage signaling for parsing done. (Mail::decryptVerify_o): Call the parser synchronously.
This is very ugly but might help some users who are affected
by regular crashes when reading crypto mail.