gspawn: Reset signal handlers for synchronous spawning
gspawn: Reset signal handlers for synchronous spawning

We should by default reset signal handlers; particularly with the
ability to install them via g_unix_signal_source_new(), we don't
want to call a user callback inside a fork()ed helper process.

https://bugzilla.gnome.org/show_bug.cgi?id=652072

mzabaluev/glib,ieei/glib,tamaskenez/glib,antono/glib,pstglia/platform-external-bluetooth-glib,mzabaluev/glib,krichter722/glib,gale320/glib,MathieuDuponchelle/glib,krichter722/glib,lukasz-skalski/glib,zsx/glib,krichter722/glib,djdeath/glib,johne53/MB3Glib,cention-sany/glib,johne53/MB3Glib,lukasz-skalski/glib,gale320/glib,darren-clark/android_platform_external_bluetooth_glib,MathieuDuponchelle/glib,pstglia/platform-external-bluetooth-glib,iConsole/Console-OS_external_bluetooth_glib,cosimoc/glib,gale320/glib,gale320/glib,01org/android-bluez-glib,ieei/glib,zsx/glib,endlessm/glib,justinkb/aosp-bluez.glib,cosimoc/glib,tamaskenez/glib,Distrotech/glib,MathieuDuponchelle/glib,antono/glib,justinkb/aosp-bluez.glib,cosimoc/glib,antono/glib,djdeath/glib,cention-sany/glib,ieei/glib,bluez-android/glib,tamaskenez/glib,djdeath/glib,01org/android-bluez-glib,darren-clark/android_platform_external_bluetooth_glib,pstglia/platform-external-bluetooth-glib,pstglia/external-bluetooth-glib,bluez-android/glib,ieei/glib,gale320/glib,MathieuDuponchelle/glib,endlessm/glib,tchakabam/glib,justinkb/aosp-bluez.glib,krichter722/glib,tchakabam/glib,mzabaluev/glib,bluez-android/glib,endlessm/glib,cention-sany/glib,darren-clark/android_platform_external_bluetooth_glib,tamaskenez/glib,djdeath/glib,mzabaluev/glib,johne53/MB3Glib,cention-sany/glib,tchakabam/glib,pstglia/external-bluetooth-glib,johne53/MB3Glib,johne53/MB3Glib,cosimoc/glib,iConsole/Console-OS_external_bluetooth_glib,bluez-android/glib,antono/glib,ieei/glib,pstglia/external-bluetooth-glib,cention-sany/glib,bluez-android/glib,krichter722/glib,iConsole/Console-OS_external_bluetooth_glib,pstglia/external-bluetooth-glib,tchakabam/glib,zsx/glib,Distrotech/glib,lukasz-skalski/glib,pstglia/platform-external-bluetooth-glib,cosimoc/glib,Distrotech/glib,endlessm/glib,justinkb/aosp-bluez.glib,MathieuDuponchelle/glib,darren-clark/android_platform_external_bluetooth_glib,01org/android-bluez-glib,pstglia/platform-external-bluetooth-glib,endlessm/glib,djdeath/glib,iConsole/Console-OS_external_bluetooth_glib,iConsole/Console-OS_external_bluetooth_glib,mzabaluev/glib,pstglia/external-bluetooth-glib,johne53/MB3Glib,justinkb/aosp-bluez.glib,zsx/glib,tchakabam/glib,lukasz-skalski/glib,Distrotech/glib,Distrotech/glib,lukasz-skalski/glib,01org/android-bluez-glib,darren-clark/android_platform_external_bluetooth_glib,tamaskenez/glib,01org/android-bluez-glib