(histograms, num_histograms): New.
	* hist.c (find_histogram, find_histogram_for_pc)
	(read_histogram_header): New.
	(s_lowpc, s_highpc, lowpc, highpc, hist_num_bins)
	(hist_sample): Remove.
	(hist_read_rec): Use the above, and handle multiple
	histogram records with disjoint address ranges.
	(hist_write_hist): Support several histogram records.
	(scale_and_align_entries): Adjust for multiple histograms.
	(hist_assign_samples_1): New.
	(hist_assign_samples): Use the above.
	(hist_clip_symbol_address): New.
	* hist.h (hist_check_address)
	(hist_clip_symbol_address): Declare.
	* gmon_io.c (gmon_out_read, gmon_out_write): Adjust handling
	of legacy format for multiple histogram changes.
	* corefile.c (find_call): Check for core_text_space and
	clip symbol address range here.
	* vax.c	(vax_find_call): Don't check for
	core_text_space, or clip the symbol's address range here.
	Use hist_check_address to check call's target address.
	* sparc.c: Likewise.
	* tahoe.c: Likewise.
	* i386.c: Likewise.
	* mips.c: Likewise. Also use core_text_sect->vma as the base
	address for code accesses, just like other machine-specific
	routines do.
	* gprof.texi: Adjust for the new logic.