Interpolation of non-string values into locations throws dynamic type errors

[tvdstorm]

Reproduce:

rascal>int x = 3;
int: 3
rascal>|file:///bla-<x>|
|prompt:///|(14,1,<1,14>,<1,15>): addition not supported on str and int
Advice: |http://tutor.rascal-mpl.org/Errors/Static/UnsupportedOperation/UnsupportedOperation.html|
ok
rascal>bool b = true;
bool: true
rascal>|file:///bla-<b>|
|prompt:///|(14,1,<1,14>,<1,15>): addition not supported on str and bool
Advice: |http://tutor.rascal-mpl.org/Errors/Static/UnsupportedOperation/UnsupportedOperation.html|