Compilation: Changes to compile on UNC's killdevil

This patch makes minor updates th schedcat to allow
it to compile on UNC's killdevil cluster.
JLFP: Don't charge rel-irqs to early-releasing tsk

Early releasing tasks do not use release timers, since
job J_{n+1} is released as soon as job J_n completes.
This patch updates the JLFP overhead accounting to
not include release timer interrupts for early-releasing
tasks.
Add log-uniform period distributions
Overhead model: add support for loading custom overheads from files

Rationale: callers may want system-specific overheads to be loaded
when instantiating an overhead model from a file.
Add support for loading overhead files with tasks-per-core task counts

When loading an overhead model in which the number of tasks is given
per core, it is convenient to scale up the task count while loading
the file. OA
Merge pull request #2 from GElliott/prop/early-release
Merge pull request #3 from GElliott/prop/unc-killdevil