--test_app switch for make_project is broken

[Christian Beer]

When creating a new project with the --test_app switch the script tries to copy the file '../samples/example_app/uc2' which is not present at this moment. This could be solved in two ways:

1. Test if this file exists before actually creating the project and show a message to the user that he should compile the samples first and then retry project creation.

or

2. Incorporate the samples directory in the make process so that the samples are build when the whole BOINC source is build. Create the link to libstdc++.a before this.

[davea]

(In [16129]) - Unix build system: build samples/example_app/,

and change the samples/ makefiles so that they automatically create the symbolic link to libstdc++.a Fixes #725