added mmap support unwillingly - but there's just too much stuff rely…

…ing on this (in particular the object reference decreasing when buffer released). The memory allocator for the transaction data is a naive one but fast, will need to come back to it later. By doing so, the parcel exception issue is resovled - no more transaction data corruption caused by reusing receiving buffer in IPCThreadState. Originally the issue happened like this,

Send StrictMode violation message to ActivityManager and get Reply#1

Before Reply#1 was read and processed

Somewhere in the code, called enforceInterface which sent out a enforceInterface message to the ActivityManager,

the second message back with Reply#2

and therefore the transaction data in it overwrote the one in Reply#1