Fix google breakpad for standalone.

The normal usage is to include the src/ directory of google breakpad
in your application and then include client/ARCH/handler/exception_handler.h
where ARCH is windows, mac or linux.

However, Linden Lab for some reason packaged the breakpad prebuilt
with exception_handler.h installed in ../google_breakpad/exception_handler.h
where "../google_breakpad" is the 'root' of the include tree comparable
with 'src' in the source tree of google breakpad.

Hence, instead of including 'src' one now must include '../include/google_breakpad'
which was already done correctly for non-standable, but not for
standalone (BREAKPAD_EXCEPTION_HANDLER_INCLUDE_DIR was set to '../include'
with the 'google_breakpad' and is subsequently never used: instead
BREAKPAD_INCLUDE_DIRECTORIES is used (which is set for non-standalone)).

Therefore one much not include "google_breakpad/exception_handler.h",
but just "exception_handler.h" or you rely on somehow the directory
*below* BREAKPAD_INCLUDE_DIRECTORIES to be part of the include path as
well.

Finally LL packages the prebuilt if another duplicate minidump_descriptor.h
in the include root. Also here including "minidump_descriptor.h" would
be better correct, but following the instructions by Google this time
we might as well include the original "client/linux/handler/minidump_descriptor.h".

My repo (http://github.com/AlericInglewood/3p-google-breakpad) doesn't
even put minidump_descriptor.h in the root anymore, only
exception_handler.h. The rest is an exact copy of the 'src' tree with
regard to the headers.

Tested to compile both standalone and non-standalone.

indra/llcommon/llapp.cpp

@@ -45,7 +45,7 @@
 #include "llstl.h" // for DeletePointer()
 #include "llstring.h"
 #include "lleventtimer.h"
-#include "google_breakpad/exception_handler.h"
+#include "exception_handler.h"
 
 //
 // Signal handling
@@ -70,7 +70,7 @@ void setup_signals();
 void default_unix_signal_handler(int signum, siginfo_t *info, void *);
 
 #if LL_LINUX
-#include "google_breakpad/minidump_descriptor.h"
+#include "client/linux/handler/minidump_descriptor.h"
 static bool unix_minidump_callback(const google_breakpad::MinidumpDescriptor& minidump_desc, 
                                    void* context, 
                                    bool succeeded);