Minor fix for local.cpp to not set "slave_subsystems" flag.
Set the executable bit on mesos-style.py.
Add explicit to single argument constructors in libprocess.

Applied either "explicit" or "/*implicit*/" to all single-arg
constructors in lib process that do not take the constructed type as
parameter.

Sorted out which denotation to choose by compiling mess and fixing all
the compile errors and by estimating whether implicit conversions might
be intended by the original authors.

Review: https://reviews.apache.org/r/19086