Fix some formatting errors, typos and other problems (#78)

Some notes:
- Removed a TODO note that was fixed in commit 43d9fbac.
- Removed a duplicate note about the '%l' time format in the changelog.
- Applied the following documentation fixes from Terrence J. Doyle:
  - https://www.mail-archive.com/ast-developers@lists.research.att.com/msg01852.html
  - https://www.mail-archive.com/ast-developers@lists.research.att.com/msg01856.html
- Fixed strange grammar in one of the error messages.
- Added missing options for rksh to the synopsis section.
- Applied a formatting fix from ksh93v- to the man page.
- Replaced a C99 line comment in src/lib/libast/comp/realpath.c with a
  proper comment that is valid in C89.
- Prioritize UTC over GMT in the documentation (missed by commit c9634e90).
- Add some extra information for 'ksh -R file' to the man page. This patch
  is from Red Hat: https://git.centos.org/rpms/ksh/blob/c8/f/SOURCES/ksh-20080202-manfix.patch

src/cmd/ksh93/data/builtins.c

@@ -1424,7 +1424,7 @@ USAGE_LICENSE
 	"a terminal or pipe.]"
 "[n]#[count?Read at most \acount\a characters.  For binary fields \acount\a "
 	"is the number of bytes.]"
-"[N]#[count?Read exactly \ancount\a characters.  For binary fields \acount\a "
+"[N]#[count?Read exactly \acount\a characters.  For binary fields \acount\a "
 	"is the number of bytes.]"
 "[v?When reading from a terminal the value of the first variable is displayed "
 	"and used as a default value.]"

src/cmd/ksh93/data/msg.c

@@ -48,7 +48,7 @@ const char e_timeout[]		= "timed out waiting for input";
 const char e_mailmsg[]		= "you have mail in $_";
 const char e_query[]		= "no query process";
 const char e_history[]		= "no history file";
-const char e_histopen[]		= "history file cannot open";
+const char e_histopen[]		= "cannot open history file";
 const char e_option[]		= "%s: bad option(s)";
 const char e_toomany[]		= "open file limit exceeded";
 const char e_argtype[]		= "invalid argument of type %c";