Add array start and end strings to generic_val_print_decorations

Add array start and end strings to generic_val_print_decorations

For Rust value-printing, I wanted to use generic_val_print_array, but
I also wanted to control the starting and ending strings.

This patch adds new strings to generic_val_print_decorations, updates
generic_val_print_array to use them, and updates all the existing
instances of generic_val_print_decorations.

2016-05-17  Tom Tromey  <tom@tromey.com>

	* valprint.h (struct generic_val_print_array) <array_start,
	array_end>: New fields.
	* valprint.c (generic_val_print_array): Add "decorations"
	parameter.  Use "array_start", "array_end".
	(generic_val_print) <TYPE_CODE_ARRAY>: Update.
	* p-valprint.c (p_decorations): Update.
	* m2-valprint.c (m2_decorations): Update.
	* f-valprint.c (f_decorations): Update.
	* c-valprint.c (c_decorations): Update.