fix linux compile issue

uint64_t not available in util.h depending on how headers are parsed.

Signed-off-by: Jonas Schnelli <jonas.schnelli@include7.ch>
Merge pull request #20 from jonasschnelli/fix_debian_compile_issue

fix linux compile issue
add timestamp to bp_key

timestamp will be needed for SPV mode "fast catchup" blockchain load.

Signed-off-by: Jonas Schnelli <jonas.schnelli@include7.ch>