add BeginsWith

stepmania/src/RageUtil.cpp

@@ -661,6 +661,15 @@ void StripCrnl(CString &s)
 		s.erase(s.size()-1);
 }
 
+bool BeginsWith( const CString &sTestThis, const CString &sBeginning )
+{
+	ASSERT( !sBeginning.empty() );
+
+	if( sTestThis.size() < sBeginning.size() )
+		return false;
+	return sTestThis.Left( sBeginning.size() ) == sBeginning;
+}
+
 bool EndsWith( const CString &sTestThis, const CString &sEnding )
 {
 	ASSERT( !sEnding.empty() );

stepmania/src/RageUtil.h

@@ -326,6 +326,7 @@ inline T Decrement( T a ) { --a; return a; }
 void TrimLeft(CString &str, const char *s = "\r\n\t ");
 void TrimRight(CString &str, const char *s = "\r\n\t ");
 void StripCrnl(CString &s);
+bool BeginsWith( const CString &sTestThis, const CString &sBeginning );
 bool EndsWith( const CString &sTestThis, const CString &sEnding );
 
 void StripCvs( vector<CString> &vs );	// remove all items that end in "cvs"