Defer validity checks until path gets to the remote side, where they
actually make sense. Add simple checks for download directory path to
ensure it's not relative, since one cannot know what current working
directory of the remote process is.
This should not affect non-Win32 platforms in any way.
As for Win32 (both MinGW and MSVC), this should hopefully allow for
unpatched compilation. Correct functioning is not yet guaranteed though.
On a way to factoring out OpenSSL support to a standalone file to ease
addition of other crypto libraries support in the future, move helpers
providing random numbers/data generation to crypto-utils.{c,h}. OpenSSL-
related functionality (generation of cryptographically strong random
data) is moved to crypto-utils-openssl.c.
Rename functions to follow currently accepted style:
* tr_cryptoRandBuf -> tr_rand_buffer
* tr_cryptoRandInt -> tr_rand_int
* tr_cryptoWeakRandInt -> tr_rand_int_weak
Fix rare case of invalid value being returned from tr_rand_int. Return
value for abs(INT_MIN) may be undefined and thus negative, and so
tr_rand_int will return negative value which is incorrect (out of
requested and expected range).
