you can't build the bitshares client on a pure debian stable release (7.x), you need at least the following from testing:
- gcc 4.8 (important, it doesn't complain with 4.7 but then crashes randomly...)
- boost 1.55
It is perfectly feasible to mix and match packages in debian, you can use pinning on your packages if you want, the solution I used myself is very simple. Install debian stable, install all the stuff you think you need. Then add the testing repositories to your sources.list, apt-get update and apt-get install the rest. Then you can comment again the testing repos in your sources list and you will have gone back to a system that's mostly debian stable, with the selected packages from testing.