BUILD: fix dependencies between config and compat.h

compat.h only depends on the system, and config needs compat, not the
opposite. global.h was fixed to explicitly include standard.h for LONGBITS.
MINOR: http: export the function 'smp_fetch_base32'

It's sometimes useful outside of proto_http.c.
MINOR: session: export the function 'smp_fetch_sc_stkctr'

This one is sometimes useful outside of this file.
MEDIUM: stick-table: make it easier to register extra data types

Some users want to add their own data types to stick tables. We don't
want to use a linked list here for performance reasons, so we need to
continue to use an indexed array. This patch allows one to reserve a
compile-time-defined number of extra data types by setting the new
macro STKTABLE_EXTRA_DATA_TYPES to anything greater than zero, keeping
in mind that anything larger will slightly inflate the memory consumed
by stick tables (not per entry though).

Then calling stktable_register_data_store() with the new keyword will
either register a new keyword or fail if the desired entry was already
taken or the keyword already registered.

Note that this patch does not dictate how the data will be used, it only
offers the possibility to create new keywords and have an index to
reference them in the config and in the tables. The caller will not be
able to use stktable_data_cast() and will have to explicitly cast the
stable pointers to the expected types. It can be used for experimentation
as well.
BUG/MINOR: http: base32+src should use the big endian version of base32

We're using the internal memory representation of base32 here, which is
wrong since these data might be exported to headers for logs or be used
to stick to a server and replicated to other peers. Let's convert base32
to big endian (network representation) when building the binary block.

This mistake is also present in 1.5, it would be better to backport it.
MINOR: sample: allow IP address to cast to binary

IP addresses are a perfect example of fixed size data which we could
cast to binary, still it was not allowed by lack of cast function,
eventhough the opposite was allowed in ACLs. Make that possible both
in sample expressions and in stick tables.
MINOR: sample: add new converters to hash input

From time to time it's useful to hash input data (scramble input, or
reduce the space needed in a stick table). This patch provides 3 simple
converters allowing use of the available hash functions to hash input
data. The output is an unsigned integer which can be passed into a header,
a log or used as an index for a stick table. One nice usage is to scramble
source IP addresses before logging when there are requirements to hide them.
MINOR: sample: allow integers to cast to binary

Doing so finally allows to apply the hex converter to integers as well.
Note that all integers are represented in 32-bit, big endian so that their
conversion remains human readable and portable. A later improvement to the
hex converter could be to make it trim leading zeroes, and/or to only report
a number of least significant bytes.