fix the modtime of files in the apk when signing
fix the modtime of files in the apk when signing

SignApk fixes the timestamp of the signature files it adds.  Use that
same timestamp for all the files, so that the modtime doesn't vary
from build to build.  (Incremental OTAs currently spend significant
time rewriting every .apk to do nothing but patch in timestamp
changes.)

see4ri/lolili,RR-msm7x30/platform_manifest,xorware/android_build,ND-3500/platform_manifest,Hybrid-Power/startsync,hagar006/platform_manifest,xorware/android_build,fallouttester/platform_manifest,xorware/android_build,knone1/platform_manifest,pranav01/platform_manifest,xorware/android_build,xorware/android_build