core: global io_service and scheduler

Scheduler and time are imported from ndn-cpp-dev.
Forwarder is using the new scheduler API.
Face system is not transitioned yet.

refs #1290

Change-Id: I5679cb50bbf9890a105f663b038f13951403c2b6
build: Requiring boost >=1.48 during configure step

Change-Id: I09110e9993903a3157be22948a7275c4625cd393
Refs: #1186
fw: rename "Interest rebuff" to "Interest reject"

Change-Id: I8275354a3eff6f4785187a8fb00da1d421df8460