Issue #69 "sprintf" fix and extended tests.

Author: judgej

src/Omnipay/Common/Message/AbstractRequest.php

@@ -335,7 +335,7 @@ public function getAmount()
             }
 
             // Check for rounding that may occur if too many significant decimal digits are supplied.
-            $decimal_count = strlen(substr(strrchr((string)$amount, '.'), 1));
+            $decimal_count = strlen(substr(strrchr(sprintf('%.8g', $amount), '.'), 1));
             if ($decimal_count > $this->getCurrencyDecimalPlaces()) {
                 throw new InvalidRequestException('Amount precision is too high for currency.');
             }

tests/Omnipay/Common/Message/AbstractRequestTest.php

@@ -111,8 +111,14 @@ public function testAmountPrecision()
         // This is *why* PHP sets the default precision at 6.
         ini_set('precision', 17);
         $this->assertSame('67.10', $this->request->getAmount());
+
+        $this->assertSame($this->request, $this->request->setAmount('67.01'));
         $this->assertSame('67.01', $this->request->getAmount());
+
+        $this->assertSame($this->request, $this->request->setAmount('0.10'));
         $this->assertSame('0.10', $this->request->getAmount());
+
+        $this->assertSame($this->request, $this->request->setAmount('0.01'));
         $this->assertSame('0.01', $this->request->getAmount());
     }