Removing info that Eclipse should be started from trunk/eclipse

Change-Id: I4e40bb14513930a7d2bccb2693f7f00ce4e27579
Some initial cleanup of StackTraceCreator.

It is pretty complex and hard to follow what is going on so I did
an initial pass to clean some parts so it is easier to write tests
and follow the code path.

Change-Id: I0693f8d91a4635f7397b11b284072e304cc50ef8
Review-Link: https://gwt-review.googlesource.com/#/c/5781/
Improves error messaging from Composite.

Bug: issue 6997
Change-Id: I7a479d624d67d9711fb7adc7c520997f8edd9b2b
Merge remote-tracking branch 'upstream/master'