fix comsub inside parameter expansion in here-document; fix readline longjmp botch; posix change for unset non-identifier; posix change for double quotes inside backquote comsub in here-document; add missing posix pieces to umask builtin

doc/bashref.texi

@@ -8248,6 +8248,12 @@ the @sc{posix} standard, and include things like passing incorrect options,
 redirection errors, variable assignment errors for assignments preceding
 the command name, and so on.
 
+@item
+The @code{unset} builtin with the @option{-v} option specified returns a
+fatal error if it attempts to unset a @code{readonly} or @code{non-unsettable}
+variable, or encounters a variable name argument that is an invalid identifier,
+which causes a non-interactive shell to exit.
+
 @item
 A non-interactive shell exits with an error status if a variable
 assignment error occurs when no command name follows the assignment
@@ -8434,6 +8440,13 @@ arguments corresponding to floating point conversion specifiers, instead of
 Bash removes an exited background process's status from the list of such
 statuses after the @code{wait} builtin is used to obtain it.
 
+@item
+A double quote character (@samp{"}) is treated specially when it appears
+in a backquoted command substitution in the body of a here-document that
+undergoes expansion.
+That means, for example, that a backslash preceding a double quote
+character will escape it and the backslash will be removed.
+
 @end enumerate
 
 There is other @sc{posix} behavior that Bash does not implement by