Quote-less file names in error messages

Hello,

The recent commit 2da74d8d640 added the following new messages:

+ libpq_append_conn_error(conn, "could not open ssl keylog file %s: %s",
+ libpq_append_conn_error(conn, "could not write to ssl keylog file %s: %s

However, I believe our convention is to quote file names in such messages.

The attached patch 0001 fixes this issue.

While working on this, I found a few other instances of the same
issue:

- A WARNING message in `fd.c` seems worth fixing (0002).

- Two DEBUG2 messages in `xlog.c` seem less important to fix (0003).

- I don't think it's worth bothering with those in developer tools (0004).

Please find the attached patches.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center