Update configure.ac

Added ubuntu 13.10 and libboost1.54-all-dev incompatibility instruction to the existing no boost_sleep warning.
Update build-unix.md

Added incompatibility and instruction regarding Ubuntu 13.10 and libboost1.54-all-dev
Merge pull request #3542

69843c8 Update build-unix.md (Christopher Latham)
720731d Update configure.ac (Christopher Latham)