fixes #116 and jumps to page if provided via argument.

[grexe]

first attempt, todo:

• test with open documents and jump to page
• check why alert does not work on page parsing error
• translation of said alert

[humdingerb]

Alerts normally don't start with the app's name, here "BePDF:".
The starndard button label to acknowledge an alert is "OK".

[humdingerb]

I tried what suggested at #116.

Neither the system BePDF, nor the one compiled with this patch react on the message hey BePDF '_RRC' with "bepdf:page_num"=11

I tried while displaying a PDF with <11 pages and >11 pages.

[grexe]

I just aligned with existing BePDF, should I fix this, too? Would need a change to translations, as the "BePDF:" prefix is used in the message.

[grexe]

I spent some quality time with hey and even compiled a debug build to find out what is going on, turns out that :

• hey can actually send a refs_received message via LOAD command (same as using _RRC for the B_REFS_RECEIVED message what code, and
• the file is specified via the file parameter and path value

this worked fine here, even jumping to different pages in the already opened document, just like I wanted :*)

hey application/x-vnd.mp-xpdf LOAD file\("/boot/home/Desktop/PDF use case/BeOS.scripting.pdf"\) with "bepdf:page_num"=int32\(2\)

I also added sanity checking for the page number and limit it to the document boundaries 1 < page_number < count_pages.

[humdingerb]

OK, I may have misunderstood the hey BePDF '_RRC' with "bepdf:page_num"=11 mention in #116 . Thought if you had a PDF open, that line was supposed to go to page 11...

Anyway, it does work fine, also when using the command line options.

If the "BePDF:" prefix and "Close" is used in alerts throughout BePDF, we dont have to start changing it here...

Let's merge! Thanks for the PR!