ftpd: fix command fetching to not do it in 1-byte reads;
 fix command de-escaping. Tested to download files with embeeded \xff and LF.
libbb: tweaks for the above

function                                             old     new   delta
ftpd_main                                           2231    2321     +90
xmalloc_fgets_internal                               190     222     +32
xmalloc_fgets_str_len                                  -      27     +27
xmalloc_fgets_str                                      7      23     +16
xmalloc_fgetline_str                                  10      26     +16
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/0 up/down: 181/0)             Total: 181 bytes

diff --git a/include/libbb.h b/include/libbb.h
index bc47ce7..8ea493b 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -594,9 +594,9 @@
 // Reads byte-by-byte. Useful when it is important to not read ahead.
 // Bytes are appended to pfx (which must be malloced, or NULL).
 extern char *xmalloc_reads(int fd, char *pfx, size_t *maxsz_p) FAST_FUNC;
-/* Reads block up to *maxsz_p (default: MAX_INT(ssize_t)) */
+/* Reads block up to *maxsz_p (default: INT_MAX - 4095) */
 extern void *xmalloc_read(int fd, size_t *maxsz_p) FAST_FUNC;
-/* Returns NULL if file can't be opened */
+/* Returns NULL if file can't be opened (default max size: INT_MAX - 4095) */
 extern void *xmalloc_open_read_close(const char *filename, size_t *maxsz_p) FAST_FUNC;
 /* Autodetects .gz etc */
 extern int open_zipped(const char *fname) FAST_FUNC;
@@ -619,6 +619,8 @@
 extern char *bb_get_chunk_with_continuation(FILE *file, int *end, int *lineno) FAST_FUNC;
 /* Reads up to (and including) TERMINATING_STRING: */
 extern char *xmalloc_fgets_str(FILE *file, const char *terminating_string) FAST_FUNC;
+/* Same, with limited max size, and returns the length (excluding NUL): */
+extern char *xmalloc_fgets_str_len(FILE *file, const char *terminating_string, size_t *maxsz_p) FAST_FUNC;
 /* Chops off TERMINATING_STRING from the end: */
 extern char *xmalloc_fgetline_str(FILE *file, const char *terminating_string) FAST_FUNC;
 /* Reads up to (and including) "\n" or NUL byte: */