GVariant: document avoiding g_variant_iter_loop
GVariant: document avoiding g_variant_iter_loop

The choice between g_variant_iter_next() and g_variant_iter_loop() is a
bit confusing for some people.  Add a note to the documentation of
g_variant_iter_loop() to clarify that it should be avoided except in a
few specific cases.

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