Add missing .ksy suffix in error message to the name of file that c…

…ould not be located

Also all other error messages starts with lower case, so adjust that's too

Fixes the test:
```
[info] - meta_imports_abs_unknown *** FAILED ***
[info]   meta_imports_abs_unknown: /meta/imports/0:
[info]   	error: Unable to find 'unknown_absolute_name' in import search paths, using: List()
[info]    did not equal meta_imports_abs_unknown.ksy: /meta/imports/0:
[info]   	error: Unable to find 'unknown_absolute_name' in import search paths, using: List() (SimpleMatchers.scala:34)
```

jvm/src/main/scala/io/kaitai/struct/formats/JavaClassSpecs.scala

@@ -55,7 +55,7 @@ class JavaClassSpecs(relPath: String, absPaths: Seq[String], firstSpec: ClassSpe
         }
       }
     }
-    throw new FileNotFoundException(s"Unable to find '$name' in import search paths, using: $absPaths")
+    throw new FileNotFoundException(s"unable to find '$name.ksy' in import search paths, using: $absPaths")
   }
 }