GRAILS-9895 - improve binding String to collection

When binding a String to a collection of some non String type, the conversion was not happening.

Relevant functional tests:
grails/grails-functional-tests@ea1dc74

Author: jeffscottbrown

grails-web/src/main/groovy/org/codehaus/groovy/grails/web/binding/GrailsDataBinder.java

@@ -925,8 +925,14 @@ else if (v!=null && (v instanceof String)) {
                 }
             }
             else if (GrailsDomainConfigurationUtil.isBasicType(associatedType)) {
-                if (isArray) {
-                    Object[] values = (Object[])v;
+                Object[] values = null;
+                if(isArray) {
+                    values = (Object[])v;
+                } else if(v instanceof String) {
+                    values = new String[]{(String)v};
+                }
+
+                if (values != null) {
                     List list = collection instanceof List ? (List)collection : null;
                     for (int i = 0; i < values.length; i++) {
                         Object value = values[i];
@@ -948,6 +954,7 @@ else if (GrailsDomainConfigurationUtil.isBasicType(associatedType)) {
                             // ignore
                         }
                     }
+                    mpvs.removePropertyValue(pv);
                 }
             }
         }