Make the default deadline gpr_inf_future to avoid mismatch between

gpr_inf_future and time_point::max(). The redundant AbsoluteDeadline prefix is removed from the utility function names.

Now the ClientContext holds a gpr_timespec instead of a time_point.

A test will be added in the server side deadline support cl.
	Change on 2014/12/11 by yangg <yangg@google.com>
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=81920769