Allow tests to be run with Pkg.test("Mongo")

This allows testing by PkgEval. Is this being maintained anymore? I am getting the following error...

```
julia> Pkg.test("Mongo")
INFO: Testing Mongo

BSON 

ERROR: error compiling BSONObject: error compiling BSONObject: could not load module libmongoc: libmongoc: cannot open shared object file: No such file or directory
 in anonymous at /home/steve/.julia/v0.3/Mongo/test/test_bson.jl:6
 in context at /home/steve/.julia/v0.3/FactCheck/src/FactCheck.jl:306
 in anonymous at /home/steve/.julia/v0.3/Mongo/test/test_bson.jl:4
 in facts at /home/steve/.julia/v0.3/FactCheck/src/FactCheck.jl:326
 in include at ./boot.jl:245
 in include_from_node1 at ./loading.jl:128
 in include at ./boot.jl:245
 in include_from_node1 at loading.jl:128
 in process_options at ./client.jl:285
 in _start at ./client.jl:354
while loading /home/steve/.julia/v0.3/Mongo/test/test_bson.jl, in expression starting on line 3
while loading /home/steve/.julia/v0.3/Mongo/test/runtests.jl, in expression starting on line 1

```