Change IsMagickTrue() to more sensible name IsStringTrue()

diff --git a/MagickCore/delegate.c b/MagickCore/delegate.c
index 2cff2b5..0c69a53 100644
--- a/MagickCore/delegate.c
+++ b/MagickCore/delegate.c
@@ -1405,12 +1405,12 @@
       {
         if (LocaleCompare((char *) keyword,"spawn") == 0)
           {
-            delegate_info->spawn=IsMagickTrue(token);
+            delegate_info->spawn=IsStringTrue(token);
             break;
           }
         if (LocaleCompare((char *) keyword,"stealth") == 0)
           {
-            delegate_info->stealth=IsMagickTrue(token);
+            delegate_info->stealth=IsStringTrue(token);
             break;
           }
         break;
@@ -1420,7 +1420,7 @@
       {
         if (LocaleCompare((char *) keyword,"thread-support") == 0)
           {
-            delegate_info->thread_support=IsMagickTrue(token);
+            delegate_info->thread_support=IsStringTrue(token);
             break;
           }
         break;