Fix image can't find error case.
   - When an exception occurs, it replaces by a file name.
   - The position of an alternative file name corrected.
Updates functions from tcpdf 4.8.006
  - Support for text-indent CSS attribute was added.
  - The following methods were added to UNDO commands (see example 47): startTransaction(), commitTransaction(), rollbackTransaction().
  - Support for the HTML "nobr" attribute was added to avoid splitting a table or a table row on two pages (i.e.: <tr nobr="true">...</tr>).
Ruby 2.0 compatibility issue
Fix link page bug on getCellCode function.
Grayscale JPEG Image Suppreted.