AppHdr.h: move warning-disabler for 4290 to before externs.h include

externs.h is where the warning is generated, so…

Signed-off-by: Steven Noonan <steven@uplinklabs.net>

Created by  Steven Noonan  on October 15, 2009
AFIBRJFF2UAQSFBKNP3JV2BH7YS72CFBPMMS263HD35VEDY4D7PQC
Change contents