changes between 0.5.7 and 0.6.2 for backporting

[dirk-thomas]

The following list of changes has been integrated into roscpp_core 0.6.2 (Lunar / Kinetic) since the last Jade / Indigo release (0.5.7).

Backported: (these changes are part of this PR)

• fix rounding error in TimeBase #49, #50
  • fix bug

Not backported:

• change semantic of duration sleep #47
  • change of sematic, high chance of breaking compatibility
• fix compiler warnings #51, #52, #53
  • changes to comply with Kinetic buildfarm, no need to backport

@ros/ros_team Please comment on the decision which changes to (not) backport.