#1 Improve const-correctness

[Markus Elfring]

Would you like to apply the advices from the article "http://en.wikipedia.org/wiki/Const-correctness" to more places in your sources?
I suggest to add the key word "const" to the type specifiers for parameters like the following.
- http://stftp.cvs.sourceforge.net/stftp/stftp/ftp.h?revision=1.3&view=markup
msg (functions "ftp_write", "send_cmd")

- http://stftp.cvs.sourceforge.net/stftp/stftp/misc.c?revision=1.12&view=markup
variable "helpmsg"
src, pat (function "str_begin")
host, dir (function "p_header")