GUID format is unspecified to allow users to choose the naming scheme.
Some restrictions however are added by this patch, mainly to ensure
coherence and memory usage.
The first restriction is on the length of GUID. No more than 127
characters can be used to prevent memory over consumption.
The second restriction is on the character set allowed in GUID. Utility
function invalid_char() is used for this : it allows alphanumeric
values and '-', '_', '.' and ':'.
Define a new module guid. Its purpose is to be able to attach a global
identifier for various objects such as proxies, servers and listeners.
A new type guid_node is defined. It will be stored in the objects which
can be referenced by such GUID. Several functions are implemented to
properly initialized, insert, remove and lookup GUID in a global tree.
Modification operations should only be conducted under thread isolation.
