Add `-dfont-export-dir=[dir]` option (issue 316860043 by address@hidden)

[lemzwerg]

LGTM.


https://codereview.appspot.com/316860043/diff/1/scm/framework-ps.scm
File scm/framework-ps.scm (right):

https://codereview.appspot.com/316860043/diff/1/scm/framework-ps.scm#newcode513
scm/framework-ps.scm:513: ;; If the cause is the file already exist,
return #f.
If the file already exists, return #f.

https://codereview.appspot.com/316860043/diff/1/scm/framework-ps.scm#newcode517
scm/framework-ps.scm:517: (_ "Font file `~a' already existed,
skipping.")
Font file `~a' already exists, skipping.

https://codereview.appspot.com/316860043/diff/1/scm/framework-ps.scm#newcode520
scm/framework-ps.scm:520: ;; If the cause is another, re-throw the
error.
`If the cause is something else, ...'

https://codereview.appspot.com/316860043/diff/1/scm/framework-ps.scm#newcode543
scm/framework-ps.scm:543: (_ "Font exporting directory `~a' already
existed.") dirname)
Font export directory `~a' already exists.

https://codereview.appspot.com/316860043/diff/1/scm/framework-ps.scm#newcode546
scm/framework-ps.scm:546: (_ "Making font exporting directory `~a'.")
dirname)
Making font export directory `~a'.

https://codereview.appspot.com/316860043/