p: Only define $slow if -s is specified as argument #1

135c2116-be2f-11e2-aa28-99ab2f7f6bcf
FLDBsum.pm: Replace call to "git hash-object" with $gitsum->add()

Works by adding "blob $size\0" before the file data.

788898a2-be3a-11e2-857f-afe173555719