Moved getenv usage across to safer osg::getEnvVar() usage

include/osg/EnvVar

@@ -17,6 +17,7 @@
 #include <osg/Config>
 
 #ifdef OSG_ENVVAR_SUPPORTED
+    #include <stdlib.h>
     #include <sstream>
 #endif
 
@@ -29,6 +30,15 @@ inline unsigned int getClampedLength(const char* str, unsigned int maxNumChars=4
     return i;
 }
 
+inline std::string getEnvVar(const char* name)
+{
+    std::string value;
+    const char* ptr = getenv(name);
+    if (ptr) value.assign(ptr, getClampedLength(ptr));
+    return value;
+ }
+
+
 template<typename T>
 inline bool getEnvVar(const char* name, T& value)
 {