native bullet build:

- change <not>istrue -> isfalse

git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@8910 75d07b2b-3a1a-0410-a2c5-0572b91ccdca

engine/nbproject/build-bullet-natives.xml

@@ -58,7 +58,7 @@
         <available file="build/bullet-base-mingw/libLinearMath.a" property="haveBulletLibraryMingw"/>
         <available file="build/bullet-base-mingw-64/libLinearMath.a" property="haveBulletLibraryMingw64"/>
         <condition property="doDownloadBulletSource">
-            <not><istrue value="${haveBulletSource}"/></not>
+            <isfalse value="${haveBulletSource}"/>
         </condition>
         <condition property="doBuildMacBase">
             <and>