* libguile/print.c (print_r7rs_extended_symbol): Print any unicode
graphic character other than '|' or '\' unescaped. Escape any spacing
character other than ASCII space.
* libguile/print.c (scm_print_opts): Add 'r7rs-symbols' print option.
(symbol_has_extended_read_syntax): If the 'r7rs-symbols' option is
enabled, then disallow '|' and '\' from bare symbols.
(print_extended_symbol): Use 'scm_lfwrite' and 'scm_putc' instead of
'display_string' and 'display_character' when printing ASCII literals.
(print_r7rs_extended_symbol): New static function.
(scm_i_print_symbol_name): If the 'r7rs-symbols' option is enabled,
use 'print_r7rs_extended_symbol' instead of 'print_extended_symbol'.
* libguile/private-options.h (SCM_PRINT_R7RS_SYMBOLS_P): New macro.
(SCM_N_PRINT_OPTIONS): Increment.
* doc/ref/api-evaluation.texi (Scheme Write): Mention 'r7rs-symbols'
print option.
* test-suite/tests/print.test ("write"): Add tests.
* module/ice-9/pretty-print.scm (generic-write)[wr]: Handle read macros
that appear in the middle of a list.
* test-suite/tests/print.test (prints?): New macro.
("pretty-print"): New test prefix.
* module/ice-9/pretty-print.scm (truncated-print): Set
`%default-port-encoding' to the encoding of PORT. Choose either
U+2026 or "..." depending on PORT's encoding.
* test-suite/tests/print.test ("truncated-print")[tprint]: New ENCODING
argument. Update existing tests accordingly. Add UTF-8 tests.
* doc/ref/misc-modules.texi (Pretty Printing): Mention the possible use
of U+2026.
