This fixes some of the warnings emitted by a compiler, when
-Wparentheses flag is used.  For readability reasons I limited a scope
of the patch to assignments used as a truth value, leaving out warnings
over a precedence of logical operators.  Example of a code, that the
warning is emitted for:

if (t = map)

I was bit hesitant with sending a patch.  How multiple parentheses
affect readability of a code for users with screen readers?  If this
patch has negative impact, I wil understand if it isn't commited.
Still diff is work looking alone for possible mistypes of an equality
operator.

Bellow is diffstat information regarding patch - first number describes
inserted lines, second deleted lines, followed by filename. 

$ git diff --numstat
6       6       src/buffers.c
3       3       src/cookies.c
1       1       src/fetchmail.c
8       8       src/format.c
5       5       src/html.cpp
4       4       src/http.c
1       1       src/jsdom.cpp
2       2       src/jsloc.cpp
1       1       src/main.c
7       7       src/sendmail.c
7       7       src/stringfile.c
4       4       src/url.c

-- 
Paul Onyschuk