check return value of RB_INSERT; ok + memleak fix by op@

move got_errors[] table into a single compilation unit (error.c) ok stsp

for portability, handle errno variations upon open(2) failure with O_NOFOLLOW Problem pointed out by naddy for FreeBSD -portable. Discussed with millert, thomas adam, and naddy.

switch to strerror_r(3) in error.c for thread-safety

introduce got_custom_error array to support multiple errors in flight This is still not thread-safe but at least avoids errors overwriting each other in single-threaded contexts.

add got_error_fmt() got_error_fmt() could eventually replace got_error_path() which has already been used to construct errors with strings that are not actually paths... ok millert@

add got_error_from_errno_fmt() for more flexibility in error messages suggested by and ok millert

use size_t for loop indices to avoid signedness warnings; from emaste@freebsd

fix NULL deref in got_error_from_errno via got_error_uuid (found by jasper)

error.c: use <limits.h> instead of <sys/param.h>

introduce got_error_path()

rename got_error_prefix_errno() to got_error_from_errno()

got_error_set_errno: take a char arg to pass to got_error_prefix_errno $> got rm a got: : No such file or directory becomes $> got rm a got: /path/to/a: No such file or directory

got_error_from_errno -> got_error_prefix_errno also add got_error_prefix_errno2 and got_error_prefix_errno3 which should hopefully all be merged into a single function with variadic args (but can't alloc mem)

error: introduce got_error_prefix_errno for better errno messages