mysqld-debug.exe in 5.5.3 on windows

Fix:

- Do not rename PDB, install mysqld.pdb matching 
mysqld-debug.exe into bin\debug subdirectory

- Stack tracing code will now additionally look in 
debug subdirectory of the application directory 
for debug symbols.

- Small cleanup in stacktracing code: link with 
dbghelp rather than load functions dynamically 
at runtime, since dbghelp.dll is always present.

- Install debug binaries with WiX