Add LD_PRELOAD for libsigchain.so to the environment

To remove the need to modify the bionic dynamic linker, add the
signal chaining library as a preload in the environment.  This
will be picked up by the dynamic linker and will override
sigaction and sigprocmask to allow for signal chaining.

Change-Id: I6e2d0628b009bd01e0ed9aed0b311871b9c8363a
system/window.h: add deprecation warnings

Change-Id: I38de3d281f28e0750b4abb86f28509f98dfc7a72
Updated trace.h to recognize ATRACE_TAG_BIONIC.

Bug: 15116468
Change-Id: If8d4971505ffe5cbc193c6ad71618a5adb8192b6
Merge "system/window.h: add deprecation warnings"
Merge "Updated trace.h to recognize ATRACE_TAG_BIONIC."
Merge "Add LD_PRELOAD for libsigchain.so to the environment"
String16.cpp rm unused utils/Debug.h

Change-Id: Ie7e3695770f20be33738a0f0a868cc914248d91a
Merge "String16.cpp rm unused utils/Debug.h"
auto-merger: merge in from aosp/master