Update epanet.c

Problem when compiling the DLL using the MSVC++ 2010 Express. 

Proposed change: Define `int iPoint;' before the for-loop

Error message reference: 
1>epanet.c(1767): error C2143: syntax error : missing ';' before 'type'
1>epanet.c(1767): error C2143: syntax error : missing ';' before 'type'
1>epanet.c(1767): error C2143: syntax error : missing ')' before 'type'
1>epanet.c(1767): error C2143: syntax error : missing ';' before 'type'
1>epanet.c(1767): error C2065: 'iPoint' : undeclared identifier
1>epanet.c(1767): warning C4552: '<' : operator has no effect; expected operator with side-effect
1>epanet.c(1767): error C2065: 'iPoint' : undeclared identifier
1>epanet.c(1767): error C2059: syntax error : ')'
1>epanet.c(1767): error C2143: syntax error : missing ';' before '{'
1>epanet.c(1768): error C2065: 'iPoint' : undeclared identifier
1>epanet.c(1769): error C2065: 'iPoint' : undeclared identifier
1>epanet.c(1770): error C2065: 'iPoint' : undeclared identifier
1>epanet.c(1771): error C2065: 'iPoint' : undeclared identifier