Fix prefixed shared strings XML file (#450)

A prefixed sharedStrings.xml file was not properly read, as we were comparing the un-prefixed name with the possible prefixed name.
Also, this commit contains a fix for sheets with rows not starting at column A.

tests/Spout/Reader/XLSX/ReaderTest.php

@@ -112,6 +112,22 @@ class ReaderTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals($expectedRows, $allRows);
     }
 
+    /**
+     * @return void
+     */
+    public function testReadShouldSupportPrefixedSharedStringsXML()
+    {
+        // The sharedStrings.xml file of this spreadsheet is prefixed.
+        // For instance, they use "<x:sst>" instead of "<sst>", etc.
+        $allRows = $this->getAllRowsForFile('sheet_with_prefixed_shared_strings_xml.xlsx');
+
+        $expectedRows = [
+            ['s1--A1', 's1--B1', 's1--C1', 's1--D1', 's1--E1'],
+            ['s1--A2', 's1--B2', 's1--C2', 's1--D2', 's1--E2'],
+        ];
+        $this->assertEquals($expectedRows, $allRows);
+    }
+
     /**
      * @return void
      */
@@ -169,6 +185,21 @@ class ReaderTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals($expectedRows, $allRows);
     }
 
+    /**
+     * @return void
+     */
+    public function testReadShouldSupportFilesWithRowsNotStartingAtColumnA()
+    {
+        // file where the row starts at column C:
+        // <row r="1"><c r="C1" s="0" t="s"><v>0</v></c>...
+        $allRows = $this->getAllRowsForFile('sheet_with_row_not_starting_at_column_a.xlsx');
+
+        $expectedRows = [
+            ['', '', 's1--C1', 's1--D1', 's1--E1'],
+        ];
+        $this->assertEquals($expectedRows, $allRows);
+    }
+
     /**
      * @return void
      */