glib-compile-schemas: check for undefined refs
glib-compile-schemas: check for undefined refs

For child schemas, verify that the named schema actually exists and
issue a warning if not.  This error in schema files will cause runtime
errors when iterating over the list of child schemas and attempting to
instantiate each one.

This will move from being merely a warning to a hard error in the
future.

Bug #646039.

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