don't prepend *compiler-path* to assembly name

The following console output illustrates the bug fixed in this commit:

```
    c:\github\VideoDump>(set CLOJURE_COMPILE_PATH=bin) & Clojure.Compile.exe program
    Compiling program to bin -- 366 milliseconds.
    
    c:\github\VideoDump>dir bin
     Volume in drive C has no label.
     Volume Serial Number is C201-2D30
    
     Directory of c:\github\VideoDump\bin
    
    06/20/2013  12:16 PM    <DIR>          .
    06/20/2013  12:16 PM    <DIR>          ..
    06/20/2013  11:58 AM             4,608 bin_SLASH_program.exe
    06/20/2013  11:58 PM             6,144 program.clj.dll
                   3 File(s)         15,360 bytes
                   2 Dir(s)  114,253,045,760 bytes free
````

`GenClass.GenerateClass` should not prepend the `*compiler-path*` to the
assembly name that is given to `GenContext.CreateWithExternalAssembly`;
the latter method already accounts for the `*compiler-path*` when
determining where to place the generated assembly.