fix clear() (clear red/invalid status)

src/qt/bitcoinamountfield.cpp

@@ -55,6 +55,12 @@ void BitcoinAmountField::setText(const QString &text)
     }
 }
 
+void BitcoinAmountField::clear()
+{
+    amount->clear();
+    decimals->clear();
+}
+
 bool BitcoinAmountField::validate()
 {
     bool valid = true;

src/qt/bitcoinamountfield.h

@@ -18,6 +18,8 @@ public:
 
     void setText(const QString &text);
     QString text() const;
+
+    void clear();
     bool validate();
     // Qt messes up the tab chain by default in some cases (issue http://bugreports.qt.nokia.com/browse/QTBUG-10907)
     // Hence we have to set it up manually

src/qt/qvalidatedlineedit.cpp

@@ -35,3 +35,9 @@ void QValidatedLineEdit::markValid()
 {
     setValid(true);
 }
+
+void QValidatedLineEdit::clear()
+{
+    setValid(true);
+    QLineEdit::clear();
+}

src/qt/qvalidatedlineedit.h

@@ -10,6 +10,7 @@ class QValidatedLineEdit : public QLineEdit
     Q_OBJECT
 public:
     explicit QValidatedLineEdit(QWidget *parent = 0);
+    void clear();
 
 protected:
     void focusInEvent(QFocusEvent *evt);

src/qt/sendcoinsentry.cpp

@@ -68,7 +68,7 @@ void SendCoinsEntry::clear()
 {
     ui->payTo->clear();
     ui->addAsLabel->clear();
-    ui->payAmount->setText(QString());
+    ui->payAmount->clear();
     ui->payTo->setFocus();
 }