[Rd] Misleading error message for quartz.save (PR#10406)

[christoph.bonitz at gmail.com]

Full_Name: Christoph Bonitz
Version: 2.5.1
OS: Mac OS 10.4
Submission from: (NULL) (84.112.127.131)


When trying something like this:

quartz.save("/path/and/filename.pdf",type=pdf)
(notice: type=pdf instead of the correct type="pdf")

the error message is:

"Filename must be a string."

The filename actually *is* a string, the *file type* isn't, therefore the
message is misleading. Change to something like

"File type must be a string"