SI-7938 - parallel collections should use default ExecutionContext

Parallel collections now use `scala.concurrent.ExecutionContext`
by default.

The `ExecutionContextTaskSupport` is optimized to use the
`ForkJoinPool` underlying the `ExecutionContext` if possible.
Otherwise, a fallback `TaskSupport` that creates a reduction tree and
execute an operation through `Future`s is used.
Don't use runtime reflection from the batch compiler.

Not only does this save a big chunk of time on startup by avoiding
classloading and symbol table population, but it also seems to
improve steady state performance of the compiler.

Theory: JIT can optimize more aggressively without the
SynchronizedXxx decorators and the like being in the classloader.
See "Class Heirarchy Analyis" in [1]

This commit does this by:

  - Avoiding use of FromString in pattern matcher, instead
    using an established mechanism to parse system properties.
  - Changes FromString back to use OptManifest. AFAICT, this
    is now only a dependency of scala.tools.cmd.gen.Codegen,
    so this is just a defensive measure.

The REPL still uses runtime reflection, so will pay a little
performance tax.

Benchmark:

    avg shortest 10 times 744ms  # before
    avg shortest 10 times 675ms  # after

[1] https://wikis.oracle.com/display/HotSpotInternals/PerformanceTechniques
from Issue #3098

from Issue #3098, some typos.
Merge pull request #3099 from yinxusen/patch-1

Fix typo in ParIterableLike
Merge pull request #3086 from axel22/topic/pc-execution-context

 - parallel collections should use default ExecutionContext
Merge pull request #3095 from retronym/topic/opt-no-runtime-reflect

Don't use runtime reflection from the batch compiler.
Updated Eclipse .classpath of partest and scaladoc projects

The version of some of the dependencies used in partest and scaladoc projects
did not match the version defined in `version.properties`. This prevented the
above projects from compiling correctly because the old dependencies were not
available in the local maven repository.
Removed Eclipse .project and .classpath for `plugintemplate` project

According to @gkossakowski this project doesn't need to be imported (and,
furtheremore, importing it in the current form results in errors in Eclipse),
hence I'm removing it.
Updated instructions for setting up Eclipse for Scala development
Merge pull request #3104 from dotta/update-eclipse-setup-instructions

Update eclipse setup instructions