Signal handler code in the style of ioquake3

registerHandler code has been put inline, and functions related to it
have changed names: signalhandler -> Sys_SigHandler, printBacktrace ->
Sys_Backtrace
Signal handler code in the style of ioquake3 …

registerHandler code has been put inline, and functions related to it
have changed names: signalhandler -> Sys_SigHandler, printBacktrace ->
Sys_Backtrace