Reduce pressure on GC by using a Traversable instead of a Seq

[romainreuillon]

Listing file using contentOf primitive return a Sequence. In large projects building many concurrent bundles in parallels this put a lot of pressure on the GC. This patch uses a Traversable instead of a Seq to reduce this pressure.

[romainreuillon]

@mdedetrich I just changed * for _ in the import statements

[mdedetrich]

@romainreuillon I just released sbt-osgi 0.9.9 which has this improvement. Should be available in maven in an hour.

[romainreuillon]

:+1: