Fix #864: Hide reflective call proxies in scalajsp by default
Fix #906: Remove accessor flags on exporter methods.

The accessor flags triggered sbt warnings for exported setters, since
they don't have the proper type (return type is Any instead of
Unit). Removing the accessor flag removes the warning and is also
better, since exporters are not accessors.
Merge pull request #913 from gzm0/refl-proxy-filter

Fix #864: Hide reflective call proxies in scalajsp by default
Merge pull request #917 from gzm0/sbt-warns

Fix #906: Remove accessor flags on exporter methods.