sxw imp patch

Hello,

the attached patch fixes a few issues in the OpenWriter importer.

- Style props are no longer deleted before they are applied, so e.g.
font size for headings is preserved. This triggered a problem when
font size is given in %, based on parent style. It's handeled now.

- The styles stream was read twice. Not really a bug but certainly
takes a tiny bit longer when importing.

- Type of font was passed to abi as "font-face". I changed it to
"font-family", this seems to be what abi understands.

Line 354 was changed to
static const char magic[10] =
{'P','K',0x03,0x04,0x14,'\0','\0','\0','\0','\0'};
before diff-ing because otherwise diff would think it's a binary
file. This is not in the patch but could be added easily.

I didn't find a bug for this, but could certainly open one if you'd
prefer.

Thanks for patiently answering all my questions on #abiword and not
loosing patience ;-)
Rob