[DOC] shell startup files, clarifications and fixes.

When Bash is started non-interactively, it runs the script pointed by
the BASH_ENV environment variable, not .bashrc.  While at it, mention
Z shell in the warning too, and mention non-interactive mode
explicitly.

gdb/doc/
2013-11-06  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Starting) <set/show startup-with-shell>: Mention
	non-interactive mode.
	(Environment) <shell startup files warning>: Mention
	non-interactive mode.  Mention .zshenv for Z shell, and talk about
	BASH_ENV instead of .bashrc for BASH.

gdb/doc/ChangeLog

@@ -1,3 +1,11 @@
+2013-11-06  Pedro Alves  <palves@redhat.com>
+
+	* gdb.texinfo (Starting) <set/show startup-with-shell>: Mention
+	non-interactive mode.
+	(Environment) <shell startup files warning>: Mention
+	non-interactive mode.  Mention .zshenv for Z shell, and talk about
+	BASH_ENV instead of .bashrc for BASH.
+
 2013-10-29  Nicolas Blanc  <nicolas.blanc@intel.com>
 
 	* gdb.texinfo (Commands to Specify Files): Add description

gdb/doc/gdb.texinfo

@@ -2139,9 +2139,10 @@ During startup program terminated with signal SIGSEGV, Segmentation fault.
 @noindent
 which indicates the shell or the wrapper specified with
 @samp{exec-wrapper} crashed, not your program.  Most often, this is
-caused by something odd in your shell's initialization file---such as
-@file{.cshrc} for C-shell, $@file{.zshenv} for the Z shell, or the
-file specified in the @samp{BASH_ENV} environment variable for BASH.
+caused by something odd in your shell's non-interactive mode
+initialization file---such as @file{.cshrc} for C-shell,
+$@file{.zshenv} for the Z shell, or the file specified in the
+@samp{BASH_ENV} environment variable for BASH.
 
 @kindex set disable-randomization
 @item set disable-randomization
@@ -2305,14 +2306,15 @@ rather than assigning it an empty value.
 @end table
 
 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
-the shell indicated
-by your @code{SHELL} environment variable if it exists (or
-@code{/bin/sh} if not).  If your @code{SHELL} variable names a shell
-that runs an initialization file---such as @file{.cshrc} for C-shell, or
-@file{.bashrc} for BASH---any variables you set in that file affect
-your program.  You may wish to move setting of environment variables to
-files that are only run when you sign on, such as @file{.login} or
-@file{.profile}.
+the shell indicated by your @code{SHELL} environment variable if it
+exists (or @code{/bin/sh} if not).  If your @code{SHELL} variable
+names a shell that runs an initialization file when started
+non-interactively---such as @file{.cshrc} for C-shell, $@file{.zshenv}
+for the Z shell, or the file specified in the @samp{BASH_ENV}
+environment variable for BASH---any variables you set in that file
+affect your program.  You may wish to move setting of environment
+variables to files that are only run when you sign on, such as
+@file{.login} or @file{.profile}.
 
 @node Working Directory
 @section Your Program's Working Directory