*TM-REVISION* --> thread-safety

[lgiessmann]

make the variable *TM-REVISION* thread-safety, since it is accessed during reading and writing (also in the restful interface);

solution define a function *TM-REVISION-R* that uses a the reader lock and a function *TM-REVISION-W* that uses the writer-lock; both function should access the variable *TM-REVISION* that should be declared as private; change all occurrences of *TM-REVISION*

[lgiessmann]

the same for *CURRENT-XTM* *DOCUMENT-ID*

[lgiessmann]

the same for *JSON-XTM*

[lgiessmann]

A possible solution could be a local let-variable named *TM-REVISION* that is initialized with the current version and hides the actual global variable d:*TM-REVISION*

[lgiessmann]

the implemented method works, sonce *TM-REVISION* is not used in the hunchentoot-handlers, because an explicit revision is given