Don't filter time stamps through the resolution supported

Don't filter time stamps through the resolution supported
by struct stat; keep them to full nanosecond resolution.
This affects behavior only on older hosts or file systems
that have lower-resolution time stamps.
* src/common.h (OLDER_STAT_TIME): Parenthesize arg.
(OLDER_TAR_STAT_TIME): New macro.
(code_timespec): New function.
(BILLION, LOG10_BILLION, TIMESPEC_STRSIZE_BOUND): New constants.
* src/compare.c (diff_file): Use full time stamp resolution.
* src/create.c (start_header, dump_file0): Likewise.
(start_header, dump_file0): Adjust to new structure layout.
(dump_regular_finish): Simplify by using timespec_cmp.
* src/extract.c (struct delayed_set_stat): Don't store stat info
that we don't need, to save space.  All uses changed.
(struct delayed_set_stat, struct delayed_link, file_newer_p):
(create_placeholder_file, extract_link, apply_delayed_links):
Use full time stamp resolution.
(check_time): Use code_timespec rather than rolling our own code.
(set_stat, delay_set_stat): Arg now points to tar_stat_info to
avoid losing time information.  All callers changed.
* src/list.c (read_and, decode_header, print_heaeder):
Use full time stamp resolution.
* src/misc.c (code_timespec): New function.
* src/tar.h (struct tar_stat_info): Record atime, mtime, ctime
separately, for benefit of hosts with lower resolution.
* src/update.c (update_archive): Use full time stamp resolution.
* src/xheader.c (code_time): Use new code_timespec function
to simplify code.
(atime_coder, atime_decoder, ctime_coder, ctime_decoder):
(mtime_coder, mtime_decoder): Use full time stamp resolution.

Report time stamps to full resolution in environment.
Report memory allocation failures rather than ignoring them.
* src/system.c (time_to_env): New function.
(oct_to_env, str_to_env, chr_to_env): Report memory allocation failures.
(stat_to_env): Report full resolution in time stamps.