Document thread-safety issues in C callbacks
Merge pull request #5657 from timholy/teh/doc_callbacks

Document thread-safety issues in C callbacks
windows: fix .julia path
fix #5798
Fix #5804 so eigs works on matrices with dimension less than 6
Merge pull request #5808 from malmaud/n5804

Fix #5804 so eigs works on matrices with dimension less than 6
Merged master